iPhone 3gs 16gb deleting the apps off the phone?

[Paris]

Im buying an Apple iPhone from a friend of mine thats only had it for a couple months I have no idea how it works but I have a question .. She has a ton of apps on this phone that I would want to take off of it and delete but if I delete everything shes put on the phone will I get the whole 16gb part back on the phone or once you put apps are you basically screwed and already lost the GB in it even after you delete all of them ... Trying to learn more about this new phone