how do suture zones form?

Answer 1

When you have 2 sections of continental crust coming together (example: Laurentia and Gondwanna).

You can find these in the Canadian Shield, the Appalachians, and the Himalayas, to name a few.

Sometimes suture zones can be very interesting especially if they become activated as faults.

Answer 2

They are the remnants of continental collisions, such as the one happening in the Himalayas or the European Alps.