The pattern calls for "button molds;" I have no idea what those are, and a quick google search didn't help. I just put a plain old button inside and it worked fine. For this sweater, the pattern recommends a size B crochet hook (2.25mm), which produces a nice, firm fabric. The buttons I used were 7/8" diameter.
For each button:
Chain 3, join with slip stitch to form a ring.
Round 1: 6 sc in ring
Round 2: 2 sc in each sc (12 sc)
Round 3: *1 sc in next sc, 2 sc in next sc; repeat from * around (18 sc)
Round 4 and 5: 1 sc in each sc (18 sc)
Round 6: insert button mold; *sc in next sc, skip 1 sc; repeat from * around until mold is completely covered.
sc = single crochet in US, or double crochet in British English
Once I'd made my first button, I found that there was too much empty space inside, so I eliminated Round 5. In other words, I only worked one round of single crochet after the increase rounds.
I also found it easier to work Round 6 all the way around once, and then insert my button into the cup-shaped space created. This helped keep the button from slipping out as I finished closing it up. To keep the back as flat as possible, I worked the last few stitches as slip stitches rather than as single crochets, and then left a tail long enough to use for sewing the button to the sweater.
There you have it. Like I said, easy peasy!
*Design number 27, Vogue Knitting Magazine Fall/Winter 1963