No one can see your files unless you choose to share them.
First you need to upload the files. You can do this from a browser using Actions > Upload, or you can turn on file syncing and place the files (and folders) into the Creative Cloud Files folder on your computer.
You can share a read-only view of your files (and folders) using Send Link. To stop sharing just choose Remove Public Link.
If you want others to be able to add files to a folder you can use Collaborate. To stop collaborating just remove everyone from the collaboration.