You're doing the back, front and two sleeves.
Pattern states (from various parts of patt):
BACK: Using smaller straight needles, cast on 92(102-114-124) sts.
FRONT: Work to correspond to back until armholes measure 6 (6½-7-7 ½) inches -- 82 (88-94-100) sts. The front is worked as back so if you were working this on circs you could be making both pieces at the same time being they're identical to a point.
SLEEVES: Using smaller straight needles, cast on 48 (48-50-50) sts.
As for sizing:
These directions are for small size (32-34). Changes for medium size (36-38), large size (40-42) and extra large size (44-46) are in parentheses. For men's sizes advance one step. Example: Women's medium size (36-38) is men's small size (36-38).
The 36-38 is Men's Small so you'd do the 40-42 for Med *IF* those measurements are applicable. This is an old pattern when ppl were more slender so work the numbers that apply and ignore what they're called.
Print out the entire pattern, highlight the numbers that apply to the size you're making. If necessary, strike out any numbers to ignore if they're confusing. For ex
BACK: Using smaller straight needles, cast on
92( 102-114- 124) sts.
Keeping to the knitting basics