knit 2 rows

Divide your total stitches by 4

Place a stitch marker after 1/4 of the stitches and at 3/4 of the stitches (in the example, at 22 (A) stitches and 66 (B) stitches)
when you reach stitch marker B, work a short row back (Google "how to knit a short row")
when you reach stitch marker (A) turn back around and continue knitting for 3 rows.
repeat a short row set from marker (B) back to (A) and on again.
knit 3 rows
repeat one more short row set from marker (B) back to (A), remove markers and knit on until your body measures your needed rise. The back will be a bit larger than your front, so make sure to measure accordingly.
Now we will split for the legs and crotch. Take your total stitches, subtract 8 for your crotch and then divide in half. In the example, your total stitches are 88, minus 8 = 80, divided in half is 40.

Knit 2 stitches. Place first half of stitches on stitch holder (40 in example), 4 stitches on a double pointed needle, your second half of the total on your 12" needles (40 in example) and the last 4 on a second double pointed needle.

Work Kitchener stitch on the double pointed needles for your crotch (Google "how to graft when knitting")
Tie yarn onto right stitch of your 12" circulars and knit around for (approx) needed rows to give you your necessary length for inseam. This will give you a basic rolled cuff. Let me know if you prefer a different style of cuff and I will change the pattern accordingly
Bind off leg (Google "how to bind off knitting")
Move stitches off stitch holder to 12" circular needles.
Tie yarn onto right stitch of your 12" circulars and knit around for (approx) needed rows to give you your necessary length for inseam.
Bind off leg, weave in ends. Ta da!