These stitch markers naturally can be used for knitting as well, but because they're hinged they're ideal for marking crochet stitches & beginning of rounds. Most will fit up to 8mm knitting needles depending on what type you buy.
Everything you need can be found in a bead or craft shop, invest in a pair of round nose pliers from your craft shop to make perfect loops everytime. The posts (wires) I use have a small pin head stop at the bottom & are 5cm long. These will be long enough to make a stitch holder decoration (to attach to your earring piece) approx 3.5cm long.
I usually start with a small seed bead, as some beads have holes larger than the end of the post, using a seed bead first will stop any larger ones falling off. When you're happy with your creation, you need to trim the wire so you can make the final loop to hang onto the earring piece.
Usually I trim the wire to 1cm past the last bead, that gives you a nice size loop, but if you are just learning, perhaps cut it a little longer until you get used to turning loops.
Make the hanging one the same way, no need for a starting seed bead as the loop at the bottom won't let anything past, you can then open the bottom loop & dangle something weird or wonderful from the bottom.