You have 3 tubes like this - oOo - and where they touch is the underarm where the sts are on holders. Just break it up into sections and it works out.
Put the body sts on a holder,
knit the sts of the first sleeve,
knit the next sts of the body (after the point where you put the underarm sts on the holder),
put the next body sts on a holder,
knit the other sleeve,
knit the back sts of the body.
The first round is going to look weird, but after a few of them, and with some decreases it starts looking like a sweater.