Troubles to shape neck!

Hi everyone! I am currently knitting a sweater, but I don’t understand the part where we shape the neck. Here’s what the pattern look like
To shape neck:
Next row: Work in pattern over first 31 stitches, turn and complete this side first.
Next row (wrong side): Bind off first 3 stitches, work in pattern to end.
Next row: Work in pattern to end
Next row: Now keeping pattern correct decrease one stitch at neck edge on following 3 rows, then on every alternate row following until there are 19 stitches remaining. Work even in pattern until armhole measures 7,5" from cast off edge. Bind off.
With right side of front facing, slip next 13 stitches onto stitch holder for neckband, join yarn to remaining stitches and bind off first 3 stitches, work in pattern to end.
Next row: Work in pattern to end.
Next row: Bind off first 3 stitches, work in pattern to end.
Now keeping pattern correct, decrease one stitch at neck edge on following 4 rows, then on every alternate row following until 19 stitches remaining. Work even until armhole measures same length as other side. Bind off.

Please, I am sooooo confused.
-What does “turn and complete this side first” mean?
-How to decrease stitches at neck edge?
-Where is the neck edge?
-What are alternate rows?
-How do we slip bound off stitches on a stitch holder?
-Armhole measures same length ad othher side? What does that even mean?

Welcome!
This is a set of directions that are easier to work with the sts on the needles than to read ahead of time.
You’re only going to work some of the sts on the needle, then turn as you would at the end of a row. The next row you work is the wrong side row. When you turn, that’s the neck edge as opposed to the armhole edge. For now, you’ll leave the rest of the sts on the needle and work with only the left shoulder.
You can decrease at the neck edge by knitting two sts together. I like to do this one stitch in from the edge.
Alternate rows are every other row.
When you’ve completed the decreases, continue knitting in pattern until the armhole measure 7.5 inches from the cast off.
You’re then going to slip the next 13sts to a holder, join a new strand of yarn and bind off the next 3 sts. You will be slipping live sts to the holder, not the bound off sts.
When you work the right shoulder, work until the right shoulder is 7.5 inches, same as the left shoulder.

What pattern are you making?

Thank you so much! It’s way more clear in my head now! To answer your question, I am knitting a sweater, I bought the pattern and the yarn on marymaxim.com.