iCloud

Open system preferences > iCloud you can uncheck the boxes of say for notes , calendars , photos , mails ..etc ( don't uncheck the box of keychain the passwords should be always saved on the iCloud server and secured ) .

You can turn on iCloud Drive but leave the Desktop and Documents option turned off and then put files that you want to be synced into the iCloud Drive folder in Finder. You can access that folder via the Finder "Go" menu and you can also add it to the Finder Sidebar via an option in Finder Preferences.