How do you work more stitches in the middle of a row?

I am working on a pattern I got from Red Heart called Cabled Chapeau and am a little confused with some of the instructions for the brim. I have included the full instructions for the brim below my questions.

I would really appreciate help with this! I’m making the hat as a christmas present for my little sister and this is the last portion I have to knit.

Question 1: How do you work more stitches in the middle of a row so that all cast on stitches are knit?

Question 2: How do I know which rows are the short-rows?

Question 3: At the very beginning of the instructions it says to “begin with a right side row and work in St st” does this mean I should work one row in St st and then start the short rows?

Pattern for brim:
Cast on 40 sts. Begin with a right side row, work in St st and work short-row shaping as follows:
Row 1: Knit 25, turn.
Row 2: Slip 1, p12; turn.
Row 3: Slip 1, k15; turn.
Row 4: Slip 1, p18; turn.
Continue to work in this manner, working 3 more sts at center each time until all 40 sts have been worked. Work 6 rows even in St st. Bind off 2 sts at beginning of next 10 rows-20sts. Bind off 3 sts at the beginning of next 4 rows-8sts. Bind off.

I went and looked at the pattern for your hat. The bill is made separately and then folded, lined with the plastic and sewn on the hat you made.

I don’t understand your first question. You cast on with any cast on you like to use and the row 1 they give is a right side row so it will be knit. You are going to work the brim in St st, so one side will be the smooth knit side and the other side the purl, bumpy side.

All the rows from row 1 until you have incorporated all 40 stitches into your short row shaping are short rows. Short rows are rows that are turned before you have worked clear to the end of a row like you normally do before you turn. Rows 1 to 4 that are given are all short rows but you keep working in the same way adding 3 more stitches in the middle each time before you turn until you have worked across all 40. In other words you will be doing the following: (the knit rows are the right side and the purl rows are the wrong side)

Row 1: Knit 25, turn. (exchange the needles [or needle tips if you are using a circular] in your hands like you would at the end of a row, so that you are ready to begin the next row working with the other side facing)
Row 2: Slip 1, p12; turn.
Row 3: Slip 1, k15; turn.
Row 4: Slip 1, p18; turn.
Row 5: Slip 1, k21; turn.
Row 6: Slip 1, p24; turn.
Row 7: Slip 1, k27; turn.
Row 8: Slip 1, p30; turn.
Row 9: Slip 1, k33; turn.
Row 10: Slip 1, p36; turn.
Row 11: Slip 1, k39; turn.

Now work 6 rows with no shaping keeping the stockinette going and working all 40 stitches each row.

Then you shape the other side of the brim by doing bind offs at the beginning of each row as follows: Bind off 2 sts at beginning of next 10 rows-20sts are left at this point. Bind off 3 sts at the beginning of next 4 rows-8sts are left. Bind off the 8 stitches.

The finishing tells you how to finish the bill. You fold that piece you just made in the middle, so that the fold line becomes the front edge of the bill. Insert the plastic and then sew the two edges together. Then sew the sewn together edges onto the hat in the center front.

Cute hat. Your sister will like this.

Short rows are just working part of the sts, not a special stitch, and can be worked in any stitch pattern. All the rows are stockinette stitch so just begin with a knit row on row 1. By the time you get to row 11 you will have worked all 40 sts you cast on. If you just follow the pattern with your needles and yarn you’ll see how it works out and that will answer all your questions.