Can anyone explain how to do a tuck stitch please!

I’m knitting a cardigan at the moment with double knitting wool (wendy wool) using the wendy mode pattern. To make a ridge in the pattern it is asking me to proceed with a tuck 1 - k tog next stitch on left needle with same st 3 rows below on wrong side.
It sounds a bit double dutch at the moment please advise as you can gather i am a novice who has decided to try my hand at knitting again after 10 yrs out of practice. Who would have thought i have actually managed to finish a cable arran jumper in yrs gone by .
Thankyou :doh: :doh:

Knit the next st on the L needle together with the stitch that’s 3 rows below it. You’re to do it in the purl bump, so peer over the top of your needle to the ws and find the st, put that up on your L needle if you want and knit them together.

I will give it a go and let you know how i get on thank you for getting in touch :knitting: