You may have seen a family tree before, named that because of the branch-like links between family members. You start with yourself at the bottom and work up and out, creating this tree-like finish. Above you are your parents, then from each of them are their parents and so on.
There are formatting norms that some follow, such as females going on the right and males to the left. Also you generally stick to blood relatives only, so no spouse's parents for example. But you are free to build yours as you feel.
While hand-drawing a tree is an option, the advantage of doing it online is that the layout is clear, you can add as much as you need with no paper edge limit, and everything is stored securely and can be easily shared.
If you want more help check out this guide on how genealogy works, and it can help to read how to map out your family tree.