To join the HubPages Earning program, you need to join Google Adsense or become an Amazon Associate.
To join Google Adsense, you need at least 10 good quality hubs with great content, pictures and at least 1,000 words. Amazon Associates doesn't have an entrance requirement, but the more hubs you have the more you are likely to earn (you only earn through Amazon if someone clicks on an advert and then buys an item).
My advice is to start publishing hubs, read as much as you can from HubPages Learning Center, as well read some hubs from Hubbers who have been here for a while and produce excellent work so that you can get a feel for what works here.
Good luck and welcome to HubPages.