백화점에서는 지금 세일하고 있어서 예쁜 하이힐도 많이 있어요. => There are things like lots of nice high heels as the department store is having a sale. 하이힐도 있어요 means "there are 하이힐s too". 도 in this case adds 하이힐 to the unspecified things that are expected/assumed to be there. It adds an additional item to what is already known from the context. Compare it with the case of the other common particle in this context, 이. - 하이힐이 많이 있어요 = There are lots of high heels - it sounds like high heels are either the only or the main item. - 하이힐도 많이 있어요 = There are lots of high heels as well - 도 makes it clear high heels are just one of many items. Another example. A: 나 마트 갔다 올게. I am off to go get groceries. B: 그럼 나도 같이 갈게. I'll go with you too then.

In this sentence it means there's a lot more (more than) 백화점에서는 지금 세일하고 있어서 Dept store at now sale is because 예쁜 하이힐도 많이 있어요. Pretty highheel more many is