Regardless of the length of your thesis you will need three parts: introduction, body and conclusion. However, a good thesis starts with a strong thesis statement. Your thesis statement is the sentence that defines to the reader what you will be discussing in your thesis. This should come at the end of your introduction.
Your thesis statement should be specific (it should include your topic, your main ideas and your opinion about the topic). A weak thesis statement does one of the following: a) states a fact or b) discusses both sides of an arguement equally, for example: a) the sky is blue, or b) smoking has both positive and negative effects.
Your introduction should start from a general concept, gradually, to a more specific idea (your thesis statement). Your body section should be the longest poart of your thesis. In your body section, you should discuss, expand upon and give details about the ideas in your thesis statement. Finally, your conclusion should summarise your body section, restate your thesis statement and if you want - you can finish with a final thought for the reader.
I hope that helps you. ^^
P.S. Sorry if there are spelling or grammar mistakes.......ㅠㅜ