Each hub you write and publish is your unique webpage (hosted by hubpages). Once it's indexed by the search engines, people looking for info on the internet will (hopefully) find what they are looking for in your hub. So if your hub is about green cheese, then someone who types "green cheese" into google will hopefully find your page listed and click on it.
You can also share your hub through social bookmarking (twitter, digg, facebook etc) and/or copy and paste the address in the top bar (URL) into an email if you want to share with friends.
Other hubbers may come across your hub through a variety of means. Either by clicking on your profile, through an email to your fans or through a topic they are interested in.
Hope this helps :)