You can look up people in the family tree via the Search bar above; use maiden names for females. Or click on the other menus and links at the very top or bottom of this page.
There is also a "Surname cloud" of last names on the home page that you can click on to see all the people in the family tree with that name.
When you navigate to someone's page in the family tree, you'll see several display options at the top of the page: The "Individual" tab (furthest left) gives a detailed view. Try some other tabs ("Ancestors," "Descendants," "Timeline," and "Family") for different views.
And click on the "Relationship" tab on someone's page to see graphically how that person is related to another person of interest (or to you if you're in the tree!). Just fill in the name of the other person of interest under "Person 2" and click "Calculate." For examples, see the lineages for Charlemagne and John Howland shown in the histories about them on the home page. A faster text-only alternative is to click on the down-arrow in the person's "Relationship" row; you may first need to set the "anchor" to be the other person of interest.
Don't miss the histories on the Relativity Research page.
Explore and have fun!