multiple entries for same contact in 'contacts' app

I have multiple ( 4 ) entries of each individual contact in all of my 'contacts' apps on iPhone, iPad, macbook pro, iMac 2013 and iMac 2017, as well as in icloud.com . I did a search on this before posting and saw that it had something to do with syncing to iCloud from various devices?

I'm not that technical, so can anyone let me know how to fix this. Do I do it on iCloud.com?

Or on the devices themselves?

Thanks.

Dennis