A thesis statement is basically a brief description of what you will be discussing in your paper. You don't want to be too detailed but you don't want to be broad either because this is a paper where you will be specific. Imagine that if you were searching old stacks of articles and you wanted to know about how arctic frost can affect the behavior of insects inhabiting the tundra, you would probably note the title but it would be more effective if there was a thesis statement right there in the introductions to tell you in short in a bit more detail than just the 5 letters you may see in the title.
An example of a thesis is here:
Let's say I was writing a paper on the civil war.
During the mid ninteenth century, the civil war heavily influenced the lives of women by converting them into independent land owners after their husbands were drafted, enforcing many females to take up clerical positions when there was a shortage, and providing the opportunity to saturate the medical sector which eventually led Clara Barton to organize the American Red Cross.
You should note that a paper has 5 paragraphs. 2 of them include the intro and conclusion and 3 are for body paragraphs. In your thesis, the topics for the body paragraphs are listed according to the order of discussion. These are the following topics if you can spot them clearly in the thesis statement.
1. converting them into independent land owners after their husbands were drafted
2. enforcing many females to take up clerical positions when there was a shortage
3. providing the opportunity to saturate the medical sector which eventually led Clara Barton to organize the American Red Cross
Include these topic sentences at the beginning of each's respective body paragraph so that the reader has a good idea of what you're about to discuss.
I have included the date in the thesis, a "WHAT?" (civil war affected women), a "HOW" (topic sentences), and a "WHY?" (for topic sentence one it is because the husbands went off to war). You don't go into too much detail with the "WHY?" component, just enough to explain that you did not come up with the specific topic out of nowhere. You will go into more detail on this when you analyze it in your paper within the body paragraphs.