for rosters, if your using windows 7 -
go to the start button, your user name folder, appdata folder, roaming folder, 2ksports folder, mlb2k11 folder, then the saves folder
so it looks like this - start/user/appdata/roaming/2ksports/majorleague2k11/saves - (no mods in this folder just roster files)!!!
drop the roster file in there.......................................................................^
for the rest of the mods, place those in your c:/program files x86/2sports/major league.baseball 2k11 folder. (all other mods in here)
if on xp- it should be just program files
few key things, always make a backup of what file your replacing (IMPORTANT)
thats it, if you have any problems, just say so, theres plenty of ppl around here willing to help.