Well I've been asked to show people how to make maps, and since my camera is down I have to write it out for you all.

Simply enough, if you own any Source game, you can already make a map for that particular game. However, you can't make a map for a game that you don't own (for example: you own CSS but you want to make a map for DoD, even though you don't have the game. You can't do that)

So starting from the beginning you need to goto your tools on the steam program and download Source SDK from the tools list. Don't worry about Source SDK Base since that's use for total conversion mods like Goldeneye Source or Zombie Panic.
Once this is downloaded right-click and goto properties. You should get a window with a couple buttons. Click on the "Set Launch Options" button and from there enter -engine ep1 into the text box. This allows you to have the episode 1 Configs
for Hammer, the program used for mapping.

Restart steam, and allow any update to occur. Now, go back to Source SDK and boot it up. Once it's done you get a bunch of options in a green window, such as Hammer, Model Viewer, etc. Click on Hammer and wait for it to load.
Now you are running the program to start building maps, from here on out it's easy as pie :3... not really, you still have to figure out what you are going to map and how it's going to work.

Start off by clicking File>New Map.
Now you get four screens. Each one of these screens are a different point of view of the map you are currently building. The top right is an overhead view and deals with x/y. The bottom right is the front, z/y and the bottom left should be the side x/z. The top left is the rendering of the map that you are building. Whatever you build, you will see it there.
For this guide, I'm only going to show you how to build a basic room with a spawn point and a light.

First click on the object on the left side of the screen, called block creation tool. You want to make a floor so on the X/Y screen, click and hold down the left mouse button across however many square you want the floor to be. Make sure when you are making the floor that it's flat,say one square or so. The bigger the box the more room it will take up in the final map file. You will get a white dotted line box. Right click it and then click the option Create Object. Now the room has a floor.

Next, you want walls. Since it should be different from your floor click on the browse button next to the texture box. you will get another window with a large selection of textures. If you just started playing Counter-Strike Source, then you will only be able to use whatever texture you will encounter with the stock maps or the other source games you have. Pick any of the textures in the first couple of rows. Some of the textures near the bottom have a special use for them, so don't bother with them until you are experienced enough to do so.

Now that you have your wall texture selected, it's time to build a wall. Each one of those boxes on the grid is 64*64, which is important to know because your character in CSS is the size of one of those boxes. So repeat the same process of building you floor only this time make sure it's a wall. Use the Bottom two screens for the Z direction and the top right screen for the way the walls are to go around the room. Make sure that the walls touch the floor, and are at a equal height to each other, since you don't want any leaks in your map.For the purpose of this guide, have the walls at least five squares high. Repeat the same process as above to make the objects by right clicking and you should now have the walls.

Last is the ceiling. Pretty much it's the same as the floor, just on top. So as long as it's touching the walls, you don't need to think about this to much.
So your room is complete, you now need to insert some Spawn Points. For every spawn point in the Map, you can have that many characters on the map. On the left side, click on the thing that looks like a pawn in chess called the entity tool. It's right above the block creation tool. Now on the left side you should get a drop down box saying entities. Underneath it is the collection of entities in the game. Click on that drop box and type in Info_player_terrorist. Now on your map, click the center of your room and you will get a green square that looks like a target. On the Z axis move the green square up off the ground and below the ceiling. If you put the spawn point anywhere where it's touching something, it won't work and you can't join the map.
Now that the spawn point is floating in mid air, you can now insert lights. For a simple effect like a single light bulb hanging down, where you typed in the info_player_terrorist type in light_spot. This creates a cone of light going down. Place it anywhere in the room so long as it doesn't touch the spawn point. Without the light, you would be running in darkness and only your flashlight would save you.

Now that your map is built, it's time to compile it. Under the file tab, click on save. Create name for it, Test_map001 will work for this. now that you saved it got back to file, click on run map. Check mark the box "Don't run game after compiling" Run the BSP as normal, run the VIS as fast and the VRAD as fast. Don't worry about HDR since their is no realistic lighting in this map. Now click okay and it will begin the compiling process.

After a minute or two, unless you got any errors, you can run this map. Exit SDK but leave Hammer Running. Start up CSS and create a server. Set the map as Test_map001 and let it load. If you did it all right, you'll be a terrorist in a room with a single light.
Huzzah!