"foll 4 alt rows: p"?

I don’t understand the following, please help.

“First and next foll 4 alt rows: p”

Does that mean 1, 3, 5, 7, 9 are purled and the others are knitted?

That is exactly what it means.

Yep - ‘foll’ means after, ‘alt rows’ means every other one.

Hey sorry I have another question to do with this, do I do this for 4 rows or just one?

Welcome to KH!
Work the purl on the next row and then every other row 4 times. So as noted above rows 1 then 3,5,7 and 9.