Hello Musikman and welcome aboard! I've only had Poser for a few days,I took the plunge while it was going cheap (well cheaper anyway) and I can't leave it alone. Burning the midnight oil with it tonight.
Someone else here will no doubt give you a far better explanation than me but of the downloads you have ready and waiting,M4 base is actually MIchael 4 basic model himself (same goes for V4.2 that's the Victoria base model)
Morphs are an add on extra that you have to buy,(maybe some are built in to the base model ,to be honest I've lost track now as to what was free and what I had to buy because I originally started off using them in DAZ3D a few weeks ago but just didn't take to the interface) they allow you to manipulate body parts to create different characteristics, thinner ,fatter more or less muscle,different facial expressions etc (see Arcadia's post further up the page about morphs with links for where to find them) Poses I think is a set of pre created instant poses you can use as a starting point rather than start entirely from scratch I suppose ,though just from my own brief  experience you'll learn more from posing a figure from scratch.

Anyway,like I say someone far beyond my feeble understanding will probably fill you in.My only advice would be to read through  the reference manual and the tutorial manual but don't stress about it,one step at a time and easy as she goes,and as you've already discovered,this forum is an Aladdin's cave of friendly advice and info!