Fallout 3 Expansions.

I Selected the package in the Menu ( DATA FILES) but i don know how to use it. I have to put New game? and play it again ?. THX
Answer #1
selected what? which expansion? besides the point, if it is selected it should become available after a few minutes of you starting normal gameplay…
Answer #2
after you have selected the expansion packs in the menu you should load your game (no need to start a new one)
play a few minutes and you should get a new quest, that’s it