These layers correspond to masks used for different process steps, on one hand, and on the other - they correspond to various layers in layout databases (GDSII, etc.).
There is a lot of jargon in layer name definitions, but also some common names.
Active = diffusion = moat - this is "active silicon", i.e. areas outside of isolation (usually STI isolation), where devices are formed (for example, overlap of gate poly and active corresponds to channel area of a MOSFET).
Select - I don't know.
N+ implant - areas where n+ implant is going into (you should know what is N+ and what is implant).
N+ diffusion = active AND N+ implant
(AND is a logical / boolean operation on layers).