Problems understanding pattern

Hi, I have started a pattern for v neck cardigan. I am at the stage i need to start shaping arm hole edge. I have to do this in pattern which i understand. I really must be stupid as i cant understand it. I need to know this in laymans terms.
Here goes:-1
shape armhole
next row Cast off 3 sts in pattern, pattern to end . 22 sts
next row purl.
I understand the above. Here is where i have the problem.
This is a left front side

  • work 2 rows dec 1 st at armhole edge in every row At the same time dec 1 st at the front in the next and foll alt row 19 sts.

I understand that I have to dec 1 st at the end of armhole edge but does that mean that on line 2 I have to decrease 1 st at the armhole edge and also at the end of the second line to leave me with 19 sts.
I then have more instructions for following lines which i can ask later
Please i am knitting this for My Grand nephew who is due to be born in May.

Goof question. These directions are often confusing.
If you call the next row, row 1 you would decrease at the beginning of row 1 (armhole edge) and at the end of row 1 (neck edge). On row 2, decrease only at the end of the row(armhole edge). That’ll take you to 19sts.