When I try to open System Preferences from the dock it opens directly into the iCloud pane
Does System Preferences have a badge (red 1) on it? This might indicate that iCloud is prompting you to turn on two-factor authentication. If that is the case, go to System Preferences > iCloud > and where it says “Two-factor authentication” click Continue to the right of it and then select your preferences.

For screenshots of this process and more discussion of it, see Apple Discussions – “System Preferences Dock Icon has red circle with 1”.


  


I would recommend doing research into two-factor authentication or two-step verification before turning it on. It is a high level of security that comes with greater responsibility for you to go through the steps to validate trusted devices – all of which use iCloud and need manual steps.