Hi and welcome!
3rd Row: *K 3, yarn over (y o), slip (sl) the next st as if to P, repeat from * across row ending with K 3.
The repeat here is really 4sts: the k3 and then the slip one. Every time you do the repeat, you'll increase one stitch because of the yarn over.
[U]4th Row: K 3, * insert needle through next st and y o and K 1, y o, K 1 in same st, sl both y o and st off needle (3 sts made), P 3, repeat from * across row, ending last repeat with K 3.
[/U]For row 4 you're going to start a kind of k2tog: the next stitch and the yo. Put the left needle into these two sts, pull through a loop (that's the k1), then yo, k1 all into the same stitch. Finally, drop the sts off the left needle. Here's avideothat may help. The only difference is that the knitters is working into a single stitch and you'll be working into the k1 and yarn over together.
Lovely looking shawl, btw.