You can use either 2 Circular Needles or double-pointed needles to knit in the round at small diameters.
To work in rounds, cast nine stitches on one end of the needle the same as you would on a straight needle. Check to make sure that the cast-on lays flat and smooth and is not twisted. Add a stitch marker to the end of the needle to mark the beginning of the round, and work the first round.
If you use double-pointed needles, please evenly distribute your cast-on over three or four needles, keeping one needle out to knit with. Make sure the cast-on lays flat and smooth and no stitches are twisted. If you'd like, add a stitch marker to the first needle to mark the beginning of the round. The needles either form a triangle (if you cast on to three needles) or a square (if you cast on to four needles).
For your information, I have provided the YouTube links below:
Knitting in the Round Part 1: Double Pointed Needles
Knitting in the Round Part 2: Two Circular Needles
I hope this information will help you.