On a perfectly clean gym floor at low speed you still won't make a circuit and come back exactly where you started without sensors to find the spot. But you can get close. Then every succeeding loop will be more and more off. BTW, please don't do that with a lawnmower!
You say 'newbie and hasn't got anything' so my guess is; you didn't run any examples, not even blink.
Are you new to the code, xcraft? What you need to buy may be the far smaller part of what you will need to put in.