I will not write out your paper or your introduction for you but I will help you organize your ideas into an appropriate format. The introduction to your paper should introduce the reader to the issue you are addressing and give an overview of the topics you are going to discuss. In this case, you are talking about and comparing two different classes of antibiotics: aminoglycosides and quinolones. Mention a brief overview and history of antibiotics starting with the discovery on penicillin. Then briefly mention the two different classes of antibiotics and their major structural features. Say that in your paper you will outline and compare three different major areas for both classes: mechanism of action, uses, and side effects.
You can then proceed in one of two different manners. You could either write three paragraphs, one on mechanism of action, one on uses, and one on side effects covering both antibiotics. Alternatively, you could write two larger paragraphs, one on aminoglycosides and the other on quinolone, and cover all three topics in each paragraph. Aminoglycosides act by disrupting bacterial protein synthesis, are often used intravenously (blood injections), and pose a potential fetal risk so are not used by pregnant women. Quinolones act by disrupting bacterial DNA, are used as broad spectrum antibacterial agents (particularly against resistant bacterial strains), and generally have a low incidence of acute side effects.
Finally, you should conclude your paper with a final paragraph. It should summarize the major differences and similarities between the two drug classes. If you feel that one class appears superior to the other one, you can state your conclusions and reasoning here.