You can pull it or push it or even pull the rubber band back, let go of the rubber band and it slings forward and hits the cart making it move forward.
Mass, you measure in kilograms, weight, you measure in newtons, pounds, and many other things.
There are many types of forces such as gravity, pulling, pushing and the "elastic force".
A force is something that you can measure like you can measure weight in newtons and Gravity is the force that pulls you towards the core of any planet or star. The heavier the object the more gravity pulls it to the core.