This article explains How to Access Your Mac over Internet.You first have to set up your Mac for screen sharing. Open the "Sharing" preference panel and check the box next to "Screen Sharing".
Do you want to power on your computer remotely and then control it by phone? It sounds like a Hollywood movie but it's totally doable with some preparation.
How easy it is to share files through web browsers, because web browsers are available on any computer. This article explains How to Share Files over Internet step by step.
