You want to build an autonomous robot? You need to control your motors somehow. That's where the H-Bridge comes into play.

Project page:
https://rohling-de.blogspot.com/2017/...

Buy at Amazon:

H-Bridge L298N
http://amzn.to/2uMFrKL

5V DC Motor with gearbox
http://amzn.to/2uD9r0J

Robot chassis with motors
http://amzn.to/2uE6exT

H-Bridge L9110
http://amzn.to/2vxYADL