There are two different types of entities, namely brush entities and non-brush entities, each type containing several subgroups. The screenshot to the right shows the entity creation menu containing all the subgroups available. The important ones are highlighted. Your entity menu might look different depending on what game you map for, but the highlighted entries should exist no matter what.
Brush entities are entities which need to be paired with at least one brush to work. This entity type is populating the subgroups func and trigger. To create a brush entity, first create a brush and select it, then right-click anywhere in the 2D grid to bring up the entity menu and select the entity.
- func contains entities to get brushes moving. So you will use this type of entities to create doors, elevators, moving platforms, rotating things, etc.
- trigger contains trigger entities which can trigger things like doors, lights, elevators etc. Here the brush connected to the entity will serve as the trigger area. As soon as someone enters the area, something happens. (See Linking Entities)
Non-brush entities are the ones populating the rest of the subgroups. To create a non-brush entity, just right click in the 2D view and select a subgroup which isn't func or trigger and select any entity from the sub menu and a colored (or grey) box will appear. Some entities like light are not in subgroups.
- fx entities are used to add special effects such as fire, sparks, smoke to the map.
- info usually only contains spawn point entities, i.e. places for your character to spawn. These are usually bigger boxes which have the size of the player. A map without any of these in it won't run, so they're very important.
- light entities are simply light emitting entities, for more info, see this.
- misc contains the entities misc_model and misc_model_static, used to put models (premade objects) into your map. For more info about these click here. You can usually find some game-specific entities here as well.
- target entities are all entities which need to be triggered by a trigger entity in order to do anything. With these entities, you can do some advanced things, so check out the subgroup, most entities in there are quite self explanatory.
- ammo, weapons and items are used to add the game specific items or weapons to the map.