How to configure PIC24F oscillator?
Yes, the clock chain on some of the PIC 24 is rather complicated, but it is all well explained in the datasheet and the family reference manual.  Look in the datasheet chapter for the oscillator, find what specific family reference manual chapter it refers to, then read that.  Carefully.  All of it.

Sometimes I find it useful to print out the overall clocking diagram usually in the first few pages of the oscillator chapter.  This can be useful to look at while reading other sections and filling in fields in the configuration registers and the runtime oscillator control registers.

Configuration bits are bits in special "registers" where you put static information at build time.  These bits will be coded into the HEX file and set in the part when it is programmed.  Some configuration needs to be known so that the device can run at all, so these must be set before run-time.  That's what the configuration bits are.  No, they aren't really SFRs.

The default values of all bits are clearly documented in the datasheet.  Read it.

Since the clock chain can be complicated, verifying I got it right is one of the first things I do in a new project.  After making sure the part is otherwise initialized and the runtime part of the clock chain is set up as I think it should be, I run code like this:

loop:
    btg LATB, #0    ;toggle RBO
    bra loop

Of course you pick a pin that won't hurt anything if toggled.  RB0 is just the example I picked here.

The BTG instruction takes one cycle, and BRA takes 2.  Each loop iteration therefore takes 3 cycles, and one whole period of RB0 therefore 6 cycles.  Now you look at RB0 with a scope and see if you really get the expected instruction clock frequency divided by 6.