The way Zoosk works is much like similar apps like Hot or Not and Tinder. Basically, you can view other user's profiles and quickly indicate whether you like them or not. While doing so you can take a look at the pictures and info on each profile, which usually includes age, interests, expectations, etc.
As usual for these kinds of apps, users can create search filters in order to find people who better fit their interests. This way you can, for example, find single women between 25 and 30 years old who don't smoke. You can also create a filter to find people who live in the same city as you.
Zoosk is a very interesting dating app that comes with a good user community and good number of features. If you want to have any real visibility, however, you'll most likely have to pay a bit of money.