1996 Toyota Celica Battery Cables

Electrical problem
1996 Toyota Celica 4 cyl Front Wheel Drive Manual

I know I sound like a complete and totally mechanical noob but, my question is:

1. For the Battery Cables there are 2 wires exiting from deep into the engine bay. One is thick and copper while the other is thin and silver. I am assuming that both of these cables connect to the positive terminal on battery? And where do they actually connect to in the engine bay? Starter and what else?

2. I then have a few cables that look just like thin grounding cables. They go to various spots on the Engine Block, Transmission and the Frame. Why so many different grounding spots?

My main issue was, I was doing a Battery Cable Replacement about 1 year ago, but after cutting some cables and stuff I had to Deploy for about a year and now I am home and forgot most of what it looked like before I left.