I figured it out but I need more info. Have you jumped into the middle of a pattern or what comes before the part you gave us? If you have only not given us the beginning chain 20, then I can see it clearly. You are merely beefing up a starting chain by working one side then the other side of the chain to make some sort of 3-dimensional piece. But I need to put it in perspective in case I am wrong. How much have you left out at the beginning and what kind of project is it? It would help to know if you are making a purse or an afghan or what. THanks.

Lots of slipper patterns start like this. Think of your starting chain as a line going in the direction of from toe to heel. Then, just as quirkpod said, you are crocheting on the "regular" part of the chain, and those 3 sc in the last chain help you turn the corner and you crochet along the opposite (bottom) side of the chain.

Yes, sounds like you are making the sole of a slipper or starting an oval doily or placemat. However, I do not see that you get 46 stitches that way. You make your first sc, then sc in next 20 chains (21 stitches total) then make 3 sc in next st (24 st) and then in the next 20 st (44 st) concluding with one stitch in the same chain as the first stitch was made (45 stitches). You have a problem here. I wonder if the correct stitch count should be 45 or if you needed to end up making 3 single crochets total in the first chain so that the oval you are making would be evenly round on each end. If this is the sole of a slipper, often the heel end is made a little smaller, so the pattern could have an error in the number of stitches listed. If it is a placemat, you probably need to add one more single crochet stitch to that first chain.

Yes, the only part I left out was the Ch 20--I suppose I should have added it. This is a slipper pattern and, as sheliajoyce has figured out, the stitch count is incorrect. I have since seen a corrected version that seems to be right. Thanks to all of you to explaining that line to me; I'm fairly new to crocheting and I had only done scarves and a couple blankets before. This is my first 3D piece. I hope it turns out well. Thanks to all of you for your help!

Row 1 (Right Side): Ch 1, 5 sc in ring; turn.
Row 2: Ch 2, hdc in first sc, [ch 1, hdc in next sc] 4 times;
turn.
Row 3: Ch 3, dc in first hdc, [dc in next ch-1 space, dc in
next hdc] 3 times, dc in next space, 2 dc in last hdc; turn �
11 sts.
Row 4: Ch 3, dc in first dc, ch 1, [dc in next dc, ch 1] 4
times, (dc, ch 2, dc) all in next dc to form center point, [ch
1, dc in next dc] 4 times, ch 1, 2 dc in top of ch-3; turn.
Row 5: Ch 3, dc in first dc, [ch 1, dc in next dc] 6 times,
(2 dc, ch 2, 2 dc) all in ch-2 space, [dc in next dc, ch 1] 6
times, 2 dc in top of ch-3; turn.
Row 6: Ch 1, working in front loops only, 2 sc in first dc,
sc in each dc and space to center ch-2 sp; 3 sc in ch-2
space, sc in front loop of each dc and space to last st; 2 sc
in top of ch-3; turn.
Row 7: Ch 2, 2 hdc in first sc, hdc in each sc to center sc
of 3-sc group at point; (hdc, ch 2, hdc) all in center (2nd)
sc at point, hdc in each sc to last sc; 2 hdc in last sc; turn.
Row 8: Ch 3, dc in first hdc, ch 1, skip next hdc, * dc
in next hdc, ch 1, skip next hdc; repeat from * to center
space; (2 dc, ch 2, 2 dc) all in ch-2 space, ch 1, skip next
hdc, ** dc in next hdc, ch 1, skip next hdc; repeat from ** to
last hdc; 2 dc in last hdc; turn.
Row 9: Ch 3, dc in first dc, * ch 1, dc in next dc; repeat
from * to center ch-2 space; (2 dc, ch 2, 2 dc) all in ch-2
space, ** dc in next dc, ch 1; repeat from * to last st; 2 dc
in top of ch-3; turn.
Rows 10-41: Repeat Rows 6-9.
Row 42: Repeat Row 6; do not turn but work sc evenly
across row ends of long edge, taking care to keep work
flat; join with a slip st to first sc; turn.
EDGING-Rnd 1: Ch 1, sc in first sc, ch 1, * sc in front loop
of sc just made, ch 1, skip next sc, sc in next sc, ch 1;
repeat from * around entire shawl; join with a slip st to first
sc. Fasten off. Weave in ends