Pattern Query

Hello All, I’m new to this site. I am quite an experienced knitter (41 years). I am knitting a jumper for a little boy but in this pattern there are terms I have never come across before so any help would be appreciated. I am doing the shoulders on the front and the instructions say

When work measures 23 (26-29-33) cm (9 [101⁄4- 111⁄2-13] in) [76 (86-96-110) rows total], leave the outside edge sts on hold every 2 rows as foll:
3 mths: 3 sts once, 4 sts twice.
6 mths: 4 sts 3 times.
12 mths: 4 sts once, 5 sts twice.
24 mths: 5 sts 3 times.
For each shoulder, pick up the 11 (12-14-15) sts left on hold, k 1 row, then cast off all the sts.

What on earth does this mean? I have never come across the term “leave the outside sts on hold”. I am doing the 3rd size (12 months).

Many thanks

Welcome to the forum!
This is an interesting way to make a sloped shoulder. At the armhole edge, place 4sts on a holder or scrap yarn. Finish the row and the next row to end at the armhole edge again. Slip 5 sts to a holder, finish the row and the next row and repeat the process of placing 5sts on hold on the following row.
I would work the 4 or 5 sts then place them on hold so that the yarn is ready to continue with the row.

Thank you so much, it makes perfect sense now. I will post a picture when finished. As it is such a small garment it should only take me a couple of days :sunglasses: