Generally the site you want to put it on will have their own way of importing the file. Best to look around the help stuff or FAQs etc there.

But basically, to use Facebook as an example, once you get to that 'file import' page, you see a 'browse' button, which allows you to find the file on your own PC, and then upload it. You don't really 'export it to the site from your own PC', to use the correct concept.