Step 1

To start, click the Tools tab in your Steam window. There you will find the Source SDK. If you do not want to make a map for HL2: EP 2, then select the game you do want to make a map for and double click the "Refresh SDK Content". Click continue when prompted.
Double click Hammer Editor.

Step 2

Now that Hammer is launched, we are going to need to start a new file.
File > New.

Step 3

What I like to do when I start a new map is to make the grid size a bit smaller. The default size is way too big to be of any decent use.
To resize the grid, press the button with the grid and the minus sign. Or if you're into keyboard shortcuts the bracket keys [ - smaller, ] - larger.


I've found that working with a larger grid size to make the basic environments (skyboxes, ground, walls, etc..) and make it smaller as you need to get some detail in (complex brush work, props, etc).

Step 4

To start this map out, we are going to make a floor. To do this, select the Block Creation Tool.

In the top view (top right), click and drag to create the size of the floor you want. I made my floor about 600-700 units. When you are happy with the size, press Enter. This will create the block / brush.

The best way to move around in the 3D view is to hold Space and the left mouse button. Then you can use the WASD keys to free look.

Step 5

Now that we have a floor, we should add some walls and maybe even a roof / ceiling. Using the block tool again, click and drag along the sides of the floor brush. Now go into either the Front or Right views (bottom two) and drag the up the same way we did before to make the floor.

Do this again for all sides.

Step 6

As of right now, you should have a hollow box as a room. In order for a player to be able to interact with this environment, we will need to give the player a place to start.
Select the Entity Creation Tool. By default the entity it will create is an info_player_start. Go ahead and click where you would like the player to start in the 3D view.

Step 7

This map is ready to be run! Don't forget to save you're map, and then press F9. This will bring up the compile window.

All the settings in the compile window are fine for this map. If you do not check the box for “Don’t run the game after compiling” then the game will launch and load the map automatically. Click OK to begin the compile. This map should be done compiling in a few seconds; there is not much to it yet. As more is added to your map, the longer it will take to compile.
If the map did not load, or if you checked the box to test the map start up the game you were making a map for (HL2, HL2: ep2, TF2…) and open the console (~) [If you don’t have the console enabled, go into the options > keyboard > advanced > enable developer console]. In the console type map