I can’t find any information on marking stiches. I am trying my first intermediate pattern, a tank top, and the instuctions say m, mark stitch. I’m sure this is an easy instruction, but I don’t understand how exactly to mark, or even what to mark with. Any help would be appreciated!!

You can just take a piece of scrap yarn and loop it loosely thru the stitch. There are open stitch markers, shaped kinda like a C that you can use, but I think those tend to fall off. Anything that won’t snag your material to mark your place could be used.

So you are just basically holding a stitch for later?

You’re not really holding it when you mark it. You’re leaving that little piece of yarn or marker in the stitch as a reference for later. At some point they’ll refer to the marked stitch as a place to seam, pick up stitches, whatever.

you’re marking it for reference at some other point in your knitting, not really holding it. you continue considering it a live stitch and work it as any other (unless your pattern states to do differently). you didn’t say why you are marking it - since they are saying “mark stitch” (vs. “place marker”), you must be doing something with that particular stitch later - it may be a point where you match up later to a second piece (like the diamond marks on a sewing pattern). you can mark the stitch as suggested, with a small piece of yarn - it’ll be easier to find later if you use a different color if you have it.

Yarn is good, and sometimes I use locking stitch markers.