If you've entered a person but can't see them in your family tree, you will need to change the "View Person" for the tree to one of that person's siblings, parents or grandparents. To do this, click the triangle in the lower corner of the sibling, parent or grandparent.  This turns that box gray, showing that it is the current "View Person", and shows their tree view.

The View Rule 

Only part of your tree can be seen at any given time.

The tree view for any person shows a) their siblings and siblings' spouses, b) both of their birth parents and direct grandparents, c) their spouse and any prior spouses, c) their descendants for three generations, and all current and former spouse descendants for three generations.