Download the save games you want.  Now go to the directory where you dowloaded the save games.  Copy or move the save game to the Tomb Raider directory and into the folder called SaveGame or of similar name.  Load the game and enjoy :)!

Still don't get it?  These screenshots of an example will help.

Download Directory

Tomb Raider saved games directory

Moving saved games from download directory to Tomb Raider directory.