First Jumper

I am making my first jumper, I am now on the part that says
Shape back Neck:
Next row:S/1,patt 87 sts,turn.
Working on these 88 sts only proceed as follow :
Next row: S/1,patt to last st, K1
Work 21 rows without shaping.

I am stuck on this pattern, could anyone help me please!!!

Welcome!
You’re going to work one shoulder and then return to the stitches left unworked for the other shoulder.
Slip one stitch and work 87sts in pattern, then turn as you would at the end of a row. You’ll leave sts unworked on the left hand needle but that’s ok. You’ll get to them later.
Now, slip the first stitch (this is the neck edge) and work back over the same 86sts to the armhole edge and continue knitting rows without increases or decreases…
What pattern are you making?

I am making the pattern for Lady"s Striped Dolman Sleeve Jumper. My daughter actually fancied this jumper and asked me if I can make one for her. I could not figure out how to go on on this part.when you say 87 sts you mean knit stitches , right?

I couldn’t find the pattern on Ravelry or Google. There are a couple of Drops patterns but none with the instructions you quoted.
If the 87sts have been knit sts, in previous rows, then yes, work them as knit sts. If there’s some other pattern, a lace or cable, etc., then work the 87sts as that pattern.

Maybe this pattern? Lady’s Striped Dolman Style Cardigan
If the pattern isn’t online or is a paid pattern you could post a few lines from it here to help.