In the following sentence, what is the independent clause?
poetry is a structure of writing that has many possibilities.

Independent Clause: Poetry is a structure of writing.

Dependent Clause: That has many possibilities.

Explanation:

An independent clause is a sentence fragment that can stand on its own you can walk up to someone and say "poetry is a structure of writing", but you can't just say "that has many possibilities" you need context on its own it doesn't make sense, you could say its dependent on another clause to make sense.

Hope my explanation can help you understand better for the future.