To pound the pavement is to go out and actively visit places, meet people, etc., in order to accomplish something; for example, to job-hunt by going from company to company.
pound the pavement は、例えば、仕事を探してあちこち会社を回るなど、何かを成し遂げるために、活動的に場所や人を訪ねて出かける、という意味です。
Examples
Dan didn’t waste any time after learning that he was being laid off, but started to pound the pavement the very next day.
I pounded the pavement for eight months before getting my first offer. It was a grueling job hunt.
Our sales reps are out pounding the pavement ten hours a day. On average, they make $5000 a month in commissions alone.
Mayor Knox won the election one vote at a time by pounding the pavement and meeting people on the street.