Boolean intersection

Keep only the space occupied by both input solids. Their non-overlapping portions are removed.

Before you start

Select overlapping editable meshes in Object Mode, with active modifiers applied. Intersection keeps only space shared by the operands.

Extract the common volume of two or more shapes.

Position the objects so their shared region has the shape you want to retain.
Select the operands, open Boolean in the modeling sidebar, and choose Intersect.
Inspect the remaining volume. Undo and reposition the inputs if the result is empty or much smaller than intended.

Controls	What changes
Shared region	With several operands, a region must belong to all of them to remain. Adding another object can reduce the result further.
Input spacing	Objects that only touch may have no shared volume. Use a visible overlap for the first attempt.
Result material	The result derives its material from the first operand. Review material and surface orientation after the operation.

The retained shape should match the overlap, with no unintended fragments. Inspect thin tips and new corners before applying further operations.

Open the editor and follow the steps with your own scene.