This means to get back money that you paid. You can get a refund for something that you bought at a store when you return the item:
I took those jeans back and got a refund.
Or you can get a tax refund like in the example above. You pay money for taxes to the government from each paycheck. At the end of the year, when you figure out the exact amount of tax you're supposed to pay, you may find out that you paid too much. In that case, you get a refund.