Well, you'll need to start off with a opening statement to introduce reader to your essay, like this:
Hamlet is a character written by Shakespeare that arguably is best known to the vast majority of people. He is so well known because...
Something like that.
Then, you'll need a thesis in that same paragraph (depending on length of essay, don't make it one whole page). It helps to write out your thesis like this:
The purpose my essay is to... explain/argue etc
After the "to" word, whatever you type there will be your thesis.
Your opening paragraphs MUST contain ideas that you will introduce into your essay.
Hope that helps.