Hi and welcome!
After you get the stitches onto the correct needles with 26sts on the first needle, you'll knit back and forth on these 26 heel sts for awhile until the heel is finished. You'll be knitting across, turning at the end of the needle and working back across those same sts. The heel is worked back and forth like flat knitting. Often the top and instep are worked in rounds (although not always).