2000 Daewoo Nubira Engine Oil Temp Redlining

Firstly, I am not a car person, that's why I came here. Secondly, my car is a heap
already, but the last thing I want is for the engine to blow up in my face. So I am in
Austin, TX and its consistently 90-100 degrees outside. I was driving about 50mph on
the highway access road when I noticed my temp gauge was all the way at the top,
redlining. I freaked out and pulled off then stopped my car. I checked the oil stick and
I'm all good on that. I restarted and headed to Walmart for coolant, since I figured that
might be what was needed. On the way, the gauge starts doing these crazy spikes up
to the red. It hovers there for about 15 heart-wrenching seconds, then drops rapidly
back down to the middle.  I kept my speed under 45 the whole way, but I still stopped
twice and waited about 10 minutes for my engine to cool down. Picked up the coolant,
but I don't know how to access my radiator, or what it even looks like! Any advice on
the heating problem in general would be greatly appreciated, also instructions for
adding the coolant. (LOST THE MANUAL) THANKS!!!!!