I own all apple products iPad,iphone,macbook,macmini and want to know how to sync all data on on one device.

Michael Therrien wrote:

When I change a password for one device. I would like it to change all of them seamlessly. Not sure if that is possible.

Depends on what password you are referring to. Device passcodes are independent per device so cannot be synced. Account passwords like for your Apple ID or email account would be global, and would be changed everywhere once you change it on one device.

Also when working on mail or documents on one device. And be able to finish on another. Thank you in advance

That is called Handoff. Check the Handoff section in the support document I linked to above, or click here ➡️ Use Handoff to continue tasks on your other devices - Apple Support

Handoff: Start work on one device, then switch to another nearby device and pick up where you left off.

Sync in what way?

Do the steps in the support document you posted from not cover what you want to accomplish? If so, explain in as much detail as possible what you are trying to do.

Also, read this support document ➡️ Use Continuity to connect your Mac, iPhone, iPad, and Apple Watch - Apple Support