There's 2 different ways: revenue, which is from quality (over quantity) Hubs that show good use of vocabulary and construction. Then there's the HubPages apprenticeship, which not only pays you, but the staff also improve your writing skills.
Be sure to write regularly, talk about hot topics by showing "for and against" arguments, and show a keen interest in the item you're talking about. Do this, and you can make a few pennies from HubPages.
Don't think you can make a living from it though - only a select few are making hundreds a month from this, but don't let it put you off either.