Well it all depends on how thick or think you want it. Me I use a 6. Go to your local Joann’s fabric store or Wal-mart and someone in the fabric department should be able to help you out!
I believe the size of the hook (the j-part where the yarn is caught) should be the same size as the yarn you are working with.
Unless you want a sort of “lacy-look” with an open weave, then you use a larger hook. They’ll prevent you from making tight stitches. But that’s for more experienced people.
Good luck, have fun, and try not to pull the stitches too tight.
The easiest way is to find a pattern for something you would like to make. The pattern will tell you what type of yarn and which crochet hook to use, and it will also explain how to determine the correct gauge so that the project will turn out to be the right size. However, if you have never done this before, you may want to get some scrap yarn and a medium crochet hook, and practice the basic stitches. Just play with it because it takes some figuring out. Have fun!
for an beginner I would reccommend a size g hook and worsted weight yarn
when working on my baby blankets i like to choose an ‘g’ hook its just big enough to make the patterns stand out. When working on afgans for adults or any 4 ply yarn i stick to and ‘i’ hook. But if you pick and easy patter like the square stitch they will tell what works best with what yarn types.