New to knitting

Hello. I’m new to knitting and I have been doing so well until now. My pattern says

Cast on 3 Sts at beg of next and foll 2 alt rows, the. 9 sts at beg of foll alt row. 63 sts

I already have 45 sts on the needle. How do I do these alt rows?

Welcome to the forum and to knitting!
If you call the next row, row 1, then you’ll cast on 3sts at the beginning of rows 1,3 and 5. Cast on 9sts at the beginning of row 7.

What are you making? Can you give us the pattern name?