Photo 2: Leave a tail and use it as a spare yarn to cast on the required number of stitches with Invisible method. (Invisible cast-on is often used as the first stage of Italian cast-on. The second stage of Italian cast-on with double knitting doesn’t apply for circular beginning.)
Photo 3 shows the same cast-on using self-striping yarn at the color change: lilac stripe serves as a “tail”, blue stripe represents the main yarn attached to the skein.

Note: I knit Combined, so I don’t bother to mount my cast-on stitches with leading leg only in front. Feel free to follow the instructions for Invisible cast-on that are the most convenient for your preferred knitting method.

Photo 4: Turn, work one row in pattern distrubuting stitches to work in the round. For the sake of demonstration first row of a sample is knitted.

Photo 5: Pass the tail through the first cast-on loop making sure your stitches aren’t twisted and join in the round.

Photo 6: Work your circle as needed.

Photo 1: Pull the tail to close the hole in the middle. Weave it in later.