Seed beads can be fiddly to handle if you’re not used to them, so I suggest you start with size 8s while you learn the stitch, and then progress to 11s or even 15s. In addition to beads, you’ll need thread, a needle and sharp scissors. If you’re very new to this, I wrote a very simple guide to materials here and beads (including sizes) here.
Thread your needle with a comfortable length of thread (no more than the span of your arms).
Tan Grey’s lovely beads!