Back crossing?

Hi, this is my first post and i’m hoping someone can help. I’m trying to do a fairly complex (I think!) cable knit. I’m fine at regular cabling, but this pattern is also asking for back and front crossing. It says:

sl next 3 stitches onto cable needle and hold at back, k2, sl p st from cable needle onto left needle and p1, k2 from cable needle

Now, I’m fineup to the “k2”. But what does “sl p st from cable needle onto left needle” mean? Which purl stitch?! all i have is 3 stitches on a cable needle! Do i put the one on the left back onto the left needle after i’ve knitted 2?

Sorry if this is really simple but i’ve never seen this before and can’t find a video or any help elsewhere. Thanks very much in advance x

Yes, you’re correct. The 3 sts you have on the cable needle contain one which is purled, probably #3 on the left. Put only that one back on the L needle.

sl next 3 stitches onto cable needle and hold at back, k2, sl p st from cable needle onto left needle and p1, k2 from cable needle

I think you may be getting the idea. Just do each step they give in order. Slip the 3sts to the cable needle and hold them in back, knit the next 2 sts from the left needle, then being sure to hold the 3 sts that are on the cable needle without any twisting, put the leftmost st (it should be a purl) back onto the left needle. Now purl that stitch you just put on the left needle, then put the working yarn behind the cable needle and knit the 2 stitches from the cable needle.