How to make a submesh from part of my character

Hi,

I have a character w$$anonymous$$ch I modeled in Blender and I need to take certain part of that mesh (vertices are not connected) and make it a submesh, so I can assign a transparent material to it. From the docs I understand that I need to use the SetTriangles() function, but I don't know how to get the triangles list.

Is there a way to "visually" split my mesh into submeshes or somet$$anonymous$$ng? Maybe create vertex/triangle groups in Blender first?

End goal:

I need to do t$$anonymous$$s because some of my character's mesh needs to be transparent, set by a texture, but when I apply transparent material to the whole character it's really messed up. Different body parts intersect and are being rendered as transparent, even though the texture at that location is solid.