The confusion gets deeper. Printers use DPI and LPI.
DPI is the resolution of the printer, and LPI (lines per inch) refers to the way printers reproduce images, simulating continuous tone images by printing lines of halftone spots. The number of lines per inch is the LPI, sometimes also called line frequency. You can think of LPI as the halftone resolution.
The Abreviation DPI gets used generically for resolution though. PPI is actually LPI x 1.5, but since most of us are lazy and don't want to do that math, we just do LPI x 2 and be done with it. Most photo labs print at 150 LPI, which would be 225 PPI (DPI, or whatever you want to call it

), but 300 has become lazy standard.
Ok, in answer to your last question, you should resize them yourself, to ensure that they look just how you want. If your images are not of the 8x10 aspect ratio, they will either stretch or squish to fit, or the printer will crop them, neither of which is desireable. If you have to crop, at least do it before you print so that you can control it.
Or you can do what I do which is not crop and just print 8x12s and buy custom frames
