Writing excellent essays for university can be hard, but doesn't have to be! The most common essay type that is written in college or university is argument/persuasive essay.
In an argument essay you need to argue a point, usually based on a reading or on the learned material. First thing you will need is a Thesis Statement.
Introductory paragraph
Thesis statement is a sentence which is inserted at the end of your first paragraph of the essay and basically states your argument. For example: "Rolelessness of teens in society, men not doing enough at home, declining job security and adolescents' exclusion from adult activities are all responsible for causing stress in families."
Prior to the thesis statement you should go over the findings or the material that you've read and state your 3 main points, which we will get to in a moment.
Main points formation
How you form the three main points will be dependent on the question your teacher asks you to answer. My sample thesis statement above probably is aimed at answering: "Why do teens face stress in our society?" Therefore, my main points are part of the thesis statement already: 1) Rolelessness of teens in society; 2) Men not doing enough at home; 3) Declining job security; 4) Adolescents' exclusion from adult activities. In this case, I have four main points, but the standard is three. Your main points must be formed on your research and must support your thesis statement.
Second paragraph
The second, third and fourth paragraphs are focused entirely on your main points - one paragraph for each point. The second paragraph should state your first main point upfront and then talk about it and the supporting evidence you've found in your reading/research. You will need three supporting points to support the main point. From the example above, the first main point is: Rolelessness of teens in society. The supporting points on which I will elaborate are: 1) Teens are not allowed to work in our society; 2) Families may give individual tasks as needed to children, but this is not universally practiced by all in our society; 3) Teens are not allowed to have a family of their own at a young age, so they are denied the experience of being responsible for others. You should have three supporting points to support your main point. If you can't find three, you must have a minimum of two supporting points, but you will need to expand how much you talk about each one to fill the space in the essay. If you can't find two supporting points, then your main point is too weak and you may want to change the main point to something else.
Third paragraph
Same as the second paragraph, but states your second main point and then talks about it.
Fourth paragraph
Same as the second and the third paragraphs, but states your third main point and then talks about it.
Conclusion paragraph
The conclusion paragraph can be almost same as the first introductory paragraph. You will need to lead with a summary statement, such as: "In this essay we've discussed the many reasons the teens in our society experience stress." It summarizes generally what you've talked about. Then re-state your three main points and conclude with a re-written thesis statement. From the example above it may be something like: "All of the above are responsible for causing stress in families."