So, now what?
If you are referring to starting your tree, then first you need to add your parents, then your grandparents, and so on. At some point, you should reach an ancestor that is already in the tree, at which point it will tell you so. Add the relative from the worldwide tree, and you will be able to see all the ancestors of that relative that have been added by other users. Keep in mind that Living relatives can only be seen by the person who added them, so you won't find one of them in the tree already.
If you are a beginner at indexing, here are links to a couple of videos that will explain the process:
This is a really quick overview of how to index: https://www.youtube.com/watch?v=huuuIQiDVpY&t=2s
If you want more instruction here is a really great one from the BYU Library: https://www.youtube.com/watch?v=nGGpcwK9rd8&t=82s
You can search on YouTube and find lots of video resources for beginning indexing as well as FamilyTree.
Well, I just discovered that this was the indexing help forums. When I left my reply above, I thought I was in the general forums. Whoops!