You can identify bacteria by their differing abilities to use carbohydrates, withstand salt, produce gas and acid, produce various substances, etc. Using diagnostic media is the most interesting part of microbiology.
Some media are very colorful.
All diagnostic media begin with a basal medium such as E-broth which you can make at home. The composition of the basal medium will depend upon the objective of your diagnostic medium. Read this entire page. You will find reading books and the professional diagnostic pages of this site useful, but these professional pages have not yet been written. Remember the Basic Requirements for Media Most beginners use media containing meat or milk products for nitrogen source, yeast extract for vitamins and nucleic acid components and some sugars, and glucose for carbon and energy source.