I’m knitting “Hugo the Couch Potato Monster” in the book [U]The Big Book of Knitted Monsters[/U] On the 3rd row the intructions say "(K1 f&b, K3) around. (30 sts)
I understand what K1 f&b is, but I don’t know what the K3 is for. How do I go from 24 sts to 30 sts using K1 f&b, K3? Please help if you know how 
The instructions want you to work the round by repeats of k1fb, knit 3 stitches. Think of the k3 as a spacer between the increases. You’ll work 6 repeats with the k1fb giving you an increase of 6 sts total (from 24 to 30sts). The round will look like k1fb, k3, k1fb, k3, k1fb, k3, etc. If you need to look at the kfb, there’s a video on the Free Videos tab at the top of the page, under Increases.
Doesn’t a k1fb create twice as many stitches? Or is it that I’m supposed to do a k1fb round, then k3, then go on stitching more rounds?
Yes, it increases one st into 2 sts. When you do 6 kfb you will have increased 6 sts (24+6). So just alternate kfb with k3 on one round and you’ll have spaced out the increases and end up with the correct number of sts (30sts).
Or is it that I’m supposed to do a k1fb round, then k3, then go on stitching more rounds?
No. Do kfb, k3, kfb, k3, kfb, k3…and so on around. You alternate the inc with k3 so you’re going to be increasing every 4th st, not doubling them.