Mesh and physics are weird

Hello,
I’ve been recently starting to use ue4 and ive put the default mannequin on mixamo and rigged it. then when ive re import the mesh, few bothering questions occurred:
1.the identification of joints are weird such as below:


擷取1.PNG
2. mesh is a above ground:
擷取.PNG
3.and the physics… ˋ_ˊ

tks :wink: