Help with VPN

Hi, I am fairly new here and not really too familiar with VPN. I would like to have a more secure and anonymous connection so I am looking into a VPN. If I start using a VPN with accounts that I have been using on a non secure network, can they be linked? In other words, once I start using a VPN should I create new accounts for the sites I trade on, or can I continue using the ones I already have? What are some of the best VPN providers?