Hi. Two things:
1) Look at the top right of this window.
2) There is a difference between registring a domain name (basically, being allowed to use it) and between setting up DNS servers so that the address resolves. When you 'buy' a name you often get an option that the firm you buy this from will manage this for you. If you did not select that (e.g. because it was cheaper) then you have quite some reading to do because DNS is simple but very easy to mess up.