In this case, the garage has the ability to pump gas. It might be part of a petrol station or a facility with a gas pump in it.
Student or Learner
This seems to mean "petrol station" not your home garage, right? What's its difference from nomal "gas station"?
54)Any kid working in a garage knows you can't pump more gas into a full tank. If you add more gas, it splashes onto the ground. Likewise, your listener's brain is always full of her own thoughts, worries, and enthusiasm. If you pump your ideas into your listener's brain, which is full of her own notions, you'll get a polluted mixture, then a spill. If you want your ideas to flow into her tank, drain her tank completely first. Whenever you are discussing emotionally charged matters, let the speaker finish completely before you jump in. Count to ten if you must speak. It will seem like an eternity, but letting the angry speaker finish is the only way that she'll hear you when it’s your turn.
Once upon a time in America it was quite common for a "garage" to be the place that both sold you gasoline and did auto repairs.
Now, people generally buy gas at convenience stores, and businesses that do auto repairs are separate.