Stitch markers are used in knitting to mark a change, so you do not have to count stitches every time. Generally, they are used to mark increases, decreases, and the start of a round when doing circular knitting.
Sometimes, stitch markers have most of them the same, with one slightly different. That is done so that, you can use the identical ones for increases/decreases, and the different looking one to mark the round beginning.
Come take a look. Feel free to leave a comment regarding what you think about the markers, or the store in general.