the benefit is that your ISP doesn't know everywhere you're going and selling the data.
the drawback is it costs some money and can be slightly slower.
right. visualize the internet as a series of pipes where information flows back and forth from various sites. you send/receive info through a pipe your ISP owns and can see where that information is sent to/from. a VPN is a basically a smaller pipe within the pipe and goes to the VPN servers. your ISP can only see that you send/receive info from/to your VPN server.