There are several ways you can earn through hubpages -
Write useful hubs, the information of which people are looking for, and invite traffic through search engines -.
Then by adding your adsense account to your hubs where you are likely to get clicks to your ads seen there,
Also by adding Amazon affiliate link and if people buy anything through your hubs, you will get a commission.
If you have a Kontera account you can add that affiliate link, which may also bring some commission, if a click happens.
If you have ebay account add that affiliate link to your account, which can also bring some commission, if a sale takes place through your hub.
Hope this is helpful.