"Steam" is a comprehensive download and gaming interface created by "Valve", a game development company responsible for well-known game titles such as "Half-Life" and "Portal". Occasionally, after purchasing and downloading a game to play, you will experience things like corrupted textures, missing models or game crashing due to internal errors. One of the main ways to correct these errors is to verify your "Game Cache Files", which will replace missing files and repair any data damaged during download.
Open your Steam client and sign in to your account. Click on the "Library" section. Right-click on the game you wish to verify and select "Properties" from the drop down menu.
Click on the "Local Files" tab. Click on the "Verify Integrity Of Game Cache..." button. Steam will then begin to verify the game cache. This may take anywhere from a few minutes to half an hour, depending on the size and complexity of the game.
Wait for Steam to finish verifying the cache files. The process window will automatically close when it has completed. Restart Steam. Click on the verified game in your Library and press the "Play" button. Your game should now load without errors.
Be sure to close all other processes that are system-intensive before running the cache verification process.
Do not verify the cache of several games at the same time. This may cause more errors. Do not run cache verification while you are defragmenting or scanning for viruses.