How do I go about investing for the first time?

My teacher gave us a fake 10,000 and we have to invest it in some companies, but I need good tips on what I should do first. There’s a money prize for a 1, 2nd, and 3rd winner in our class and I really want to do well so I can win. Any tips on what I should do first? I think I’ve got my eyes set on Costco wholesale, Amazon.com, 3M co, Exxon Mobil corporation, and Monsanto…? Also, what do you think of investing in general?