Add a mesh to the level as a rigidbody or select a mesh and replace with Rigidbody
Put it in the position you want it
open its Properties (F4) and click the tiny lock button on top of window to allow you to select other things in the world.
open the Attachment rollout under Base click the green arrow, then click the Skeletal Mesh, to add the name of the mesh to the property field.
Under Base Bone Name enter the name of the bone you want to attach the mesh to. Eg. b_Hips. it will fill in the Base skeletal component.
Unclick the tiny lock
Now the mesh will move around with the actor.