AT FIRST you will have a mix of emotions. The machine is scary because you’ve never seen anything like it before. There it is, sitting there, printing something really neato out of a spool of plastic. You’ll want to jump right in and print something out for yourself. You want to use the machine. You need to use the machine.
YOUR FIRST FEW ATTEMPTS will most likely fail. This is a great thing because you will learn a lot. I highly suggest that you browse around on Thingiverse for a bit, find something that you would like to print and use that to get familiar with 3D printing.
(...used Makerbot 3D printers so far. I have seen other 3D printers but I have not spent much time with them.)