Confused

Hi all, hope ur having a great weekend.just downloaded horizon today and can open app. The problem I have is I got a registration number and don’t know where to put(if it has to go anywhere) but the other prob is have horizon on my desktop but all the games it shows when I open app are not the ones I got. How do I get the games I have for x box and get that info to horizon on my desktop . sorry for being a dumb ass but all the youtube stuff shows the games being changed that players have but don’t show how they we’re put there in the first place. Thanks very much and if even someone can point me in the direction of a good tutorial that would be great. Thanks in advance, Cliffy