Only you and people you share files/folders with can see your files. 

If you share files, then share files with a public link, anyone with the link can see your files.

If you invite people to a shared folder, then only those people can access the content.

In some special cases it can be necessary to view files to solve a specific support issue. Usually it is enough to access the metadata of the files. If not, we will let you know before we proceed troubleshooting, so you will know, and have a chance to stop further troubleshooting.