Essentially, an informative essay (also called an expository essay) simply serves to educate the reader about a particular topic, while a persuasive essay is organized around a thesis statement that asserts an opinion.  An informative essay is not intended to convince the reader of a certain position, but rather should just present facts about the topic.  A persuasive essay advocates a particular position that can be argued for or against, and that position will be expressed in a thesis statement.

The wording used in your assignment will usually indicate which type of paper you should be writing, though persuasive writing is generally more common (particularly in more advanced courses).  For tips on understanding your assignment, visit our helpful guide here.