Welcome to the addictive world of knitting!
I think plastic needles are hard to use, myself. I'd go with metal needles around a size 8 to start with for practice, with some worsted weight yarn. Just keep knitting and purling and you'll get the hang of it quickly.
Needles come in sizes from teeny tiny to big and fat, straight, circular, and double pointed. As you find things you want to knit, you'll see your needle collection growing.