We recommend that you start by reading the SAFE Network Wiki.
You might also be interested in listening to SAFE Network School, a series of podcasts that covers in depth the content of the wiki documentation.
If you want to get a high level overview of the SAFE Network, you should watch the SAFE Network Introduction video.
The other videos are also very good. Some are presentations, others are FAQ questions or tutorials.
If you want to look deeper, you should have a look at MaidSafe's whitepapers.
Keep in mind that some of the papers are not up-to-date with the current implementation of the network.
Previously, the SAFE Network was being developed in C++.