Source SDK: Mastering the Source/How do I get Source?
The Source SDK is easy to download and 100% free, and it's time you learned how to get it for yourself. it's important to know that the only way to download the Source SDK is through Steam, and you must have a Steam account to do so. Also, in order to download the Source SDK, you must first own the game you wish to edit for on Steam.
Once on Steam, click on the drop down box labeled "Games" at the top of the screen, and click "View Games Library". When you're in your Games Library you'll notice a box labeled "ALL GAMES" directly above your games list, click it and select Tools from the drop down box. This will take you to a gallery of special programs that you have access to depending on the games you own on steam. Just like we went over previously the Source SDK has many versions, so to be able to download one version, you must also own the game the SDK belongs to on Steam. Note that even if you download one of the games that works for the basic SDK, such as half-life 2, or Team Fortress 2, you can still only access the games you own. Meaning that if you have Team fortress 2, but not half-life 2, you cannot make maps for Half-life 2, even though they share the same version of the Source SDK. This is important to note, but most likely since you're here you already own the game you plan on editing for, so this will most likely not be a problem.
It's as simple as can be from here on. Locate whichever form of the SDK you wish to download, and double click it. This will then open up three windows, the first window will show you the disk space the program requires, how much disk space you have available, and an estimated download time. Click "Next", and you'll move onto the second window which presents two check boxes, one asking if you'd like a start menu shortcut for the program, and another asking if you'd like a desktop shortcut for the program. Choose whatever suits you and click "Next" and you'll move onto the third window where the download will begin. It's as simple as 1, 2, 3, literally.
Launching the Source SDK
It's important to note that the Source SDK will not appear in your Games Library after you download it. Just like before it will be located in the Tools Library, and on your desktop or start menu, depending on what you chose during the download. If you did not choose to place a shortcut during the download, you can always go back to the already downloaded program in your Tools Library, right click and select "Create Desktop Shortcut", there is no option for a start menu shortcut this way. Double click on whatever outlet you're using and the Source SDK Application Browser will open up.
All right, you've got it installed and know where to find it. Now let's move onto the Application Browser.