Rotations: Required at all schools as far as I know. You basically work at a number of different pharmacy settings as part of your schooling in your last year (or two). You maybe spend a few months at each setting. This is just to get you a feel for the different settings...maybe expose you to something you like...but mostly just to get some hands on work before they actually send you out there.
Residencies: After receiving your Pharm.D, you pick a specialty area of pharmacy and spend a year or two focusing specifically on that area alone. Allows you to work in one of those specialties once you're done with the residency. Not everyone has to do a residency. If you just want to work at Walgreens (or any other retail/community/basic pharmacy), there'd be no need for you to do one.