If they are package files, yep. :) If they are compressed, then you will have to extract them with WinRAR etc first to get the .package files out.
Also, not to confuse matters more, but I've ran across a few mods (actual mods, not custom content) that are supposed to actually stay in their .zip. The creators clearly state if that is the case, though.
Lastly, if you download any lots or sims, you'll get a zip file full of other "random" files - you extract the random files, and they go into the "Tray" folder rather than "Mods."