What are these cables in my walls for?
The cables in the top photo seem to be telephone wires, but certainly not cat5 cables. It looks like two telephone wires were connected together.

Cat5 ethernet cables always have 8 insulated wires, grouped into 4 twisted pairs. The cable is thicker and the insulation quite thin so that you can see bulges formed by the twisted pairs.

In the bottom photo I can't see the cable(s), but the colors are wrong for cat 5 cable.

More information on cat5 cable, including the proper colors, can be found e.g. here.