How to add constraint on bones?

Hi,

Does anyone here know how to add a constraint on bones? I’m doing IK right now, and I’m trying to add a constraint to a bone (that’s for my elbow) to limit the axis on which it can turn. This is specifically a hinge constraint.

It’s set up, but it’s not moving with the bone, and rather just staying in place when IK is moving.

Can anyone help?

Thanks!