How do I store all my documents online?

I want to save all my documents, word, excel, ppp etc, as well as photos and pdf’s so that I have a backup in case my computer crashes. I also want to be able to share this with my family so we can all access these documents. It is important that such a system is easy to use and get started – it should be as easy as using and saving stuff in folders on my computer. I would of course prefer a service that is free…. but if not at least inexpensive. And it has to be safe too. Does anyone have any recommendations?