Wikipedia internet help?

I don't get how on wikipedia there is an Edit button for editing articles and on the main page it says anyone can edit it. But how come it was in the newspaper someone was banned from wikipedia from editing an article? So really your not allowed to edit it but yet there is an edit button? Also how, if you are allowed to edit it does wikipedia overcome the problem of people vandalizing articles? Please help me out here.
Thanks Dragon

They overcome vandalism by banning people and patrolling for recent changes. Anyone <i>can</i> edit Wikipedia, until you vandalize an article, then there's a chance your IP will get banned. Some articles can't be edited by unregistered or newly registered users because they are the subject of repeated vandalism attempts. That's how they control vandalism.

i think youre only allowed to edit if you have a wiki account and get banned for putting false info, swearing and the like.

Their IP address was probably banned because they were making unconstructive edits. Make a good edit, or a poor edit in good faith, and you won't be banned (but will be warned about the latter). There are bots (i.e. not human editors) that can identify vandalism easily and get through thousands of reverts a day; regular users can also revert vandalism. The problem is overcome by banning people, temporarily banning editing of articles except to established users and reverts.