Ask HN: Learning movie CGI

After watching movies such as Harry Potter and Avatar, I became interested in the CGI effects used in movies. I realize that these are done by huge teams, but I want to learn about how the effects are created and how to create simple ones myself. I'm a fairly experienced programmer, but I don't know much about graphics programming and absolutely nothing about 3D modeling. Can anyone suggest some resources to learn about this? I don't even know where to begin.