If you still have the stitches on your needles you can just use your circular needles. Some people may prefer a separate needle, but you don't need one and it makes it easier.
There seems to be lots of ways of doing it which makes looking for a video confusing. Here's your instructions using your same two needles.
Cast on 3 onto left needle and knit them
Slip the 3 stitches back to the left needle as if to purl
K2, sl1 knitwise, sl1 stitch knitwise, k2tbl
Return 3 stitches to the left needle
Repeat last two rows to the end.
Once you get started you'll see it's easy.