Broken spring? Door too heavy to lift or opener cannot move it?
Garage-door springs store significant energy. Do not loosen winding cones, spring hardware, bottom brackets or lift cables without proper training and tools.

You do not need to know the exact failed part before requesting service. Describe what the door is doing, any sound you heard, whether one side is higher, and whether the opener still runs.
Send a non-emergency service request and describe what the door is doing.