How do you use titles to cheat on Fallout 3

I'm not sure what you mean by using "Titles" to cheat on Fallout 3, but if you meant the "Tilde" key on your keyboard, well that's easy enough to answer
First thing to know is that the tilde key only puts you into the console mode of the game where you enter your cheats and codes. Because the list of codes for fallout 3 cheats and console modifiers are quite extensive, please visit: http://www.bethsoft.com/bgsforums/index.php?showtopic=911922
The site above has details on what each cheat function does and even gives tips on where to find certain items such as where to find the bobbleheads, schematics, and even NPC locations.
some basic cheats I can give you are:
tgm - god mode
tcai - disables combat ai
please use these codes sparingly as they will affect the game play, and could potentially spoil the fun of the game for you.
Take care!