Garry's mod

Sandbox maps (built for building)

gm_construct: The classic default. A large grey area with textured buildings and spawn zones, perfect for building and testing.
gm_flatgrass: A big, wide, flat plane. Great for vehicles, physics experiments, and builds that need lots of room.
gm_bigcity: A sprawling urban environment, popular for roleplay and shooting scenarios.
gm_fork: A neon, techy cityscape.

npcs are docile mobs which also uses pathfind and only have small amount of health.
there are custom npcs which are also made by players.

hostile mobs can only be spawn via spawnlist these mobs attack nearby players and can be killed with guns and melee.
all hostile mobs have many hp depending on how much the players who made them give them how much hp they should have.
all hostile mobs can also have custom damage that can only be changed by the creator like the players that made them
these mobs uses pathfind towards nearby players to kill them

this is where players can download/subscribe to custom maps.
there's also custom weapons made by players which is other weapons that Can equip via spawn menu.
there's many custom maps and weapons like melee and guns.

What custom maps are
Custom maps are levels made by the community rather than by Valve or Facepunch. They’re ordinary Source engine maps (.bsp files) that give you a different place to build, roleplay, or play a game mode. Anything beyond the default maps like gm_construct and gm_flatgrass counts as custom.

custom maps can only download through workshop which all custom maps made by other players are automatically placed. this is where players can download map.

Special
Bugbait: A small, gooey pheropod from the Antlion story. When thrown, it attracts nearby antlions, so it’s mostly a novelty unless you have antlions around.

players can respawn when killed or press the "suicide/kill" button which instantly kills them and they can respawn infinitely because Garry's mod is a game and it's not fun to have a respawn mechanic. players have 100 hp

all weapons have infinite ammo
Melee
Crowbar: The iconic Half-Life tool. It’s a red metal crowbar with a hooked end, swung with left-click. It does moderate damage up close and can smash breakable props.
Stunstick: A black baton with an electric tip that sparks when it hits. It’s the Combine police weapon, a melee weapon that hits a bit harder than you’d expect.
Pistols
9mm Pistol: A small, plain-looking semi-automatic handgun with a clip of 18. It’s accurate but weak, and has no secondary fire.
.357 Magnum: A large silver-and-black revolver that holds 6 shots. It does very high damage per hit but fires slowly. Right-click zooms in with a scope view.
Automatic weapons
SMG: A compact grey submachine gun with a magazine of 45. It has a fast fire rate and low damage per bullet. Right-click launches a grenade from the underbarrel launcher (it uses separate SMG grenade ammo).
Pulse Rifle (AR2): The Combine’s large, blocky, blue-lit rifle with a 30-round magazine. Right-click fires an energy ball that disintegrates most things it hits. It has a long cooldown and uses separate ammo.
Shotgun
Shotgun: A pump-action shotgun that holds 6 shells, with a wooden-looking pump grip and tight pellet spread. Left-click fires one shell and right-click fires two at once.
Ranged and explosives
Crossbow: A rebar-style crossbow that fires metal bolts. Right-click zooms. The bolts pin NPCs and props to surfaces and glow with heat on impact.
RPG Launcher: A rocket launcher with a built-in laser pointer. The rocket follows the red dot while the laser is on. Right-click toggles the laser.
Frag Grenade: A hand grenade that explodes a few seconds after you throw it. Right-click rolls it along the ground instead of throwing it.
SLAM: A small explosive device that you can stick to walls as a laser tripwire mine, or use as a remote-detonated charge. Right-click switches between the two modes.

Overall look
The spawn menu (opened with Q) is a large, semi-transparent panel that covers most of the screen while the game stays visible behind it. The style is flat and gray/dark, with simple rectangular tabs and panels rather than anything decorative. While it’s open, your cursor is free and the game keeps running behind it.

Top bar and tabs

Across the top is a row of tabs:

Spawnlists / Props: the grid of spawnable models
Weapons: weapon icons grouped by category
Entities: items, NPC-related entities, and addon entities
NPCs: friendly and hostile characters
Vehicles: cars, boats, and other drivable objects
Post Processing: screen effects
Dupes: saved contraptions
Saves: saved game states
Tools (the “Utilities” or tool section, which the Tool Gun’s options also appear in)
The active tab is highlighted, and addons can add their own tabs to this row.

the spawn menu has medkits that CNA be use to heal players like {{user}}

Tool Gun
Body: A boxy handheld device that looks like a gun, mostly dark grey or black with a simple, industrial look.
Screen: Its signature feature is a small display on the side that shows the name of the currently selected tool (like “Weld” or “Rope”) in text.
Beam and effects: It fires a thin, short beam with a small spark or glow at the point where you aim. A small prompt near the crosshair shows what the tool does and its controls.
HUD: Besides the screen on the gun, the tool’s name, instructions, and options appear on your own HUD.

Physics Gun: Grabs, moves, rotates, and freezes props.
physics gun: a chunky, metallic, cannon-like device with a rounded, mechanical shape.
Color: The glowing parts (the core and the energy lighting) change with your weapon color setting in the player options. By default this is a bright cyan or blue, but you can set it to any color.
Front prongs: Two or more claw-like prongs at the front, which open and close when you grab something.
Beam: When you hold an object, a glowing beam in your weapon color runs from the muzzle to the object, with a bright glow where it touches. When you hold the left mouse button and move the mouse wheel or rotate with E, the beam bends and stretches as the object moves.
Freeze effect: Freezing an object (right-click) gives a short flash or sparks and tints the prop.

gravity gun: a chunky, metallic, cannon-like device with a rounded, mechanical shape.
Color: The glowing parts (the core and the energy lighting) change with your weapon color setting in the player options. By default this is a bright cyan or blue, but you can set it to any color.
Front prongs: Two or more claw-like prongs at the front, which open and close when you grab something.
Beam: When you hold an object, a glowing beam in your weapon color runs from the muzzle to the object, with a bright glow where it touches. When you hold the left mouse button and move the mouse wheel or rotate with E, the beam bends and stretches as the object moves.
Freeze effect: Freezing an object (right-click) gives a short flash or sparks and tints the prop.
Gravity Gun
Body: The standard HL2 Zero-Point Energy Field Manipulator. It has a metallic grey body with exposed mechanical parts, a prominent barrel, and a curved front.
Color: Its glow is orange or yellow, and it doesn’t follow your weapon color setting.
Prongs and core: The prongs at the front swing open and the core lights up when you pick up an object, and they close when you drop or launch it.
Effects: There’s no beam like the Physics Gun’s. Instead you see small energy particles around the muzzle, and a pulse of force when you fire a prop away.

players and {{user}} have many weapons.
there are also custom weapons only accessable through custom mods

Garry's mod is a game where players like {{user}} can do what they want. (sorry I'm too lazy and stupid to actually put more info even though I know Garry's mod but never played it?