A thesis statement announces the topic to the reader with facts like a headline.

The following sentence is a thesis statement that can easily become a 5-paragraph essay. I like baseball.

The following sentence is a thesis statement that focuses on one idea. When I was in high school, I used to play sports, and when I wasn't playing sports I would hang out with my friends and go for hikes in the mountains.

A thesis statement must not have more than one main idea.

The following sentence is a possible thesis statement because it builds the possibility of an argument or persuasive discussion. The fuel efficiency for passenger cars should be at least 50 miles per gallon.