Need Help With Contacts Please

Can anyone explain how contacts works please, and how best to set it up?

At one point, I ended up with not just duplicate contacts, but quadrooples!

1) How can I remove ALL my contacts from the sim card, keeping just what's on the device (backed up to MSD)

2) I also see duplicates caused by contacts being on the device AND on Google. Very confusing:-/

Any help explaining how the contacts list works, I'd be very grateful for.

Thanks

And why does this forum keep 'blacking out' on my laptop;-) Might Addblocker cause that?