How do I separate the body parts for a 3D Model?

I have a 3D obJ, but not sure how to separate it to the arms and legs and stuff. I downloaded 3d model rigs from the asset stores and those have the model separate into body parts like the picture below. When I got this model from another website it came in one piece. Do I have to go to blender and create like a bone structure or something and like combine it with the current mesh?

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There is loop cut tool when selecting edges/lines.