Ok real quick:
It seems like you're actually trying, unlike a few other posts I've seen
here where the OP is basically asking for someone to design a complete
board for them with very little information.
The OSCCON register sets the internal clock frequency. Just worry about
bits 6 through 4. The others shouldn't matter.
Next you have to config the pin connected to the LED as an output. Say
you want to use pin 8; you'd have to clear bit 2 of TRISC since pin 8 is
bit 2 of port C. The bits in a TRIS register must be cleared to make it
an output, and set to make it an input (think 1 for input, 0 for
output).
Sometimes there's a register that configs a pin for use with the A/D, or
as a digital pin. I don't see it on this chip.
As for the configuration bits (what is set in MPLAB, page 111 of
datasheet), make sure the watchdog is disabled for now, WDTE, and set
FOSC to binary 100. That sets it to use the internal oscillator. Make
sure the MCLR pin is pulled to +5 so it doesn't get stuck in reset.
As for the format of how to write to these registers, look at some
examples provided with HITECH. I don't recall how that one works. You
could take a look at my website. I have some example code on there for
other PICS. Actually, now that I think about it, I believe the single
digit clock I have there uses the 688.
http://users9.nofeehost.com/jmiller/