I may get this wrong so you might want to wait for someone more experienced/intelligent to confirm or deny.
I think you have the foot with a heel done. You now are going to work the leg. Correct so far? I hope so. Put the held stitches back on the needle. I guess you’re using dpn’s. Using another needle pick up and knit half of (12-14-16 = 6-7-8) the appropriate number of stitches then pick up and knit the other half with another needle. You should be ready to join in the round for knitting the leg.
The next section tells you where to place markers for decreasing and when to decrease.
Insert 1 marker in the middle of the 10 sts on middle part (= mid front on toe) and 1 marker in st at the back of heel, there are 30-32-35 sts between markers in each side. Now continue piece in the round in garter st. When piece measures 2 cm / 3/4’’, K 2 sts tog on each side of every marker on every other round (= 4 sts less per round). Continue dec until piece measures 5-5-6 cm / 2"-2"-2½". Bind off the remaining sts. Sew seams under foot in outer loops of edge sts to avoid a chunky seam.
HTH They’re cute slippers. I may make a pair.