There are many ways to accomplish that. You can enable file sharing and access the files of one computer from the other, and vice versa. You could also use
Dropbox for file sharing over the internet. If you want to share screens, I use
TeamViewer, which works with Windows, Mac OS X, Linux, Ubuntu, iPhone, iPad, etc. It's very secure and quite simple to set up and use (no messing around with ports), which comes in handy if providing remote support to those who aren't very computer literate. You can talk them through the setup on their end and be connected to them in less than a minute. It's also free for personal use. I prefer it over
LogMeIn because it includes free file transfers between computers, a feature I use frequently.