Just to be clear, the Academic Progress Rate is a D1-only concept that applies to each team within a college's athletic program. Teams meet APR by having enough players get passing grades and returning for the following term.
I suspect you're asking about Progress-Toward-Degree requirements covered in 14.4 of the division Manuals. These are different for each division, with D1 having the most stringent requiements. Both D1 and D2 have more than 4 pages of rules on this subject, so it isn't practical to summarize. D3 is very simple: the college decides if the player is making adequate progress. For NAIA, a rough summary is the player must have averaged 12 hours per term.