What does it mean to increase sales?

To sell more than you have sold in a corresponding period. A business will always want to increase sales as time goes on. So whatever amount of things they sold last month, they would hope to sell more this month. That is what it is to increase sales. They may do different things to make that happen. They may expand the range of items they sell. They may try to get more new customers. They may reduce prices. They may try to sell in more places. They may get more staff to sell. They may do special promotions of their products to get people to buy. They may do more advertising. All of these things are in an effort to increase sales.