A thesis statement is one sentence that tells the main idea of your writing. It shows what you think or what you want to explain. A thesis should respond to a research question about the topic you are investigating. This question should be arguable, meaning that it has 2 or more sides. A thesis should be backed by evidence that supports the same side. The length of the thesis should mirror the length of the paper, so if the paper is relatively short the thesis should also be short.
For example, if your topic is "online learning," a thesis could be: “Online learning helps students because it is flexible and gives easy access to lessons.”