Level Design Overview
Brushes: the Foundation of 3D Level Design
Blocks. Wedges. Cylinders. Spikes. They may not sound like much, but these are the basic building blocks of all architecture created in Hammer. You can clip, manipulate, and in some cases, carve them. You can combine these "brushes" to make any shape possible, real or imagined. (Complicated geometry may be better suited for models, however.) This is known as constructive solid geometry (CSG) and this is the editing style Hammer uses. Creating brush solids is described in the section Brush Creation.
Once you create a brush, you'll want to assign a material to it.
Entities and Entity Types
You say you want more in your game world than inanimate solids? Well then, what you want are entities. While brushes are "world objects" used to form the backbone of your level, entities are the objects that move, make sounds, and/or be interacted with. An entity is anything that performs some type of operation or task within your level.
Point entities exist at an exact point in the world. Examples include lights, monsters and players. (Monsters and players do have an area, but this is defined by the game code and is not modifiable from within the map.) Some point entities are just that: points. For example, the env_beam entity, which controls beam effects, uses two point entities as targets; you place the two points and the beam of light runs between them.
Brush entities depend on a brush created in Hammer for their physical presence. They are less common but can include doors, platforms, and other large, moving objects. Some are "triggers", which are invisible and untouchable but fire events when certain conditions are met (e.g. the player walking inside one).
The creation of both point and brush-based entities is described in Entity Creation.
Putting it All Together
Using these simple components you can create a virtually limitless variety of levels. Whether a barren room or a vast, complex world, you'll do it by using solids and textures to create your architecture, then adding models, lights, monsters, buttons, moving platforms and a host of other entities to bring your creation to life.
Once everything is in place, you will need to compile your level by choosing Run Map from the File Menu (shortcut: ). This is the process that turns your collection of solids and entities into a playable level that you can run in the Source Engine. Although the compiling process happens when you think you've finished your level, knowing something about this process ahead of time can save you many headaches.