Hi,
my old disc had crashed completely, though some friend of mine managed to save everything on it including old Sims 3 save files under CasThumbnails package and AllThumbnails package files. I installed the Sims 3 on the new disc and tried to retrieve old saved files (as he advised) via copying these two package files into Package folder (from Mods folder). These package files - that's those two I mentionned above - are they the files that include everything what was saved throughout the previous games?
I'm an absolute Sims beginner, in fact I'm asking all these questions in my daughter's name, that's why I may not know the basics.
New installation went fine, I updated the game version to 1.67. Still, this is a completely new game and I have no idea how to retrieve old saves. Maybe they were in some other files, not these two package files I mentionned???

Those aren't the saves - those two files don't matter, you can ignore them. You want the Saves folder.

You may also need the Installed Worlds folder if the save was in a world that didn't ship with the game or an EP. And Saved Sims might be nice.