The expression "pound the pavement" means to walk from place to place on streets, often in search of something. For example, the young man is pounding the pavement looking for work, means he is going to a lot of companies in search of a job. Today, of course, people mostly look on the internet for job opportunities. A young woman pounded the pavement looking for just the right gift for her boyfriend. That is, she walked all over, looking for a gift in stores. Of course, the expression only applies to searching for something in a city where there are sidewalks (pavement). One would not "pound the pavement" in search of berries in a forest or to look for an item in a large store.