Google runs lots of different systems, and they all store data about you. There's the search engine itself, of course, which knows what you've been looking for on the web. Then there's Youtube, Blogger, Calendar, your Google Drive, Hangouts, Gmail and more.

If you want to download a copy of all the data about you that's held on Google's servers, it's actually surprisingly easy. This is really useful if, say, you have a lot of important messages in your Gmail account and you want to ensure that you have a local copy. Just in case something happens to your Google account and you can no longer access them.

The key to all your data is a site called Google Takeout, which you'll find at https://takeout.google.com/settings/takeout. Just go there, log in if you haven't already done so, and then select which data you want to download.