A lot of journals supply class files. Many require adding additional packages to your installation. Inexplicably, they don't give much help installing. WTF? get with the program! Latex is supposed to be about the content, not the format. All the extra garbage ya'll require to install is the exact antipode of that idealism!
Anyway, this example will follow a revtex install over MikTeX in Windows
The download file will contain folders labeled bibtex, doc, source, and tex. Copy and paste these into the MikTex install folder (Program Files/MikTex X.X) and merge with existing. For MikTex to recognize the new packages go to
Start-All Programs-MikTeX X.X-Settings
(or Click → → → →
Click on the button "Refresh FNDB"
I referred here to figure this out.