Make a swatch (a small square of knitting at least 3 inches wide), block it, and then check your gauge. If your stitches are too small, use a needle one size bigger. If your stitches are too big, use a needle one size smaller.
You don’t always have to check your gauge (I know, you won’t anyway), but please do it on projects that you really need to fit a certain size. Watch the video to see how it’s done.
How to pick up and knit stitches in knitting:
Socks patterns and mitten patterns both call for you to pick up stitches.
Top-down socks have a heel flap which usually has a slipped-stitch edge that you need to pick up into, whereas mitten thumbs have a raw edge.