Yes, advertising works. Everything is a form of advertising from word of mouth, posters, billboards, radio, Social media and even smoke signals! If you want to attract clients you have to tell them where you are so they can find you, like you, and then buy from you When they need you.
There are multiple ways of reaching a specific client . The most important thing about reaching your market is knowing where to find them. For instance: If you are a nail salon and you target is a female age 25-54 you need to think of what type of things this client will like and enjoy. Planning a successful campaign around you target takes insider knowledge of consumer habits and characteristics.
When you think about starting your business you want to keep in mind that you spend months or years planning and organizing your business. As long as you plan on being in business you will need to do some form of advertising to continue bringing in new clients. So there is no limit on how much or often you should advertise.