So I have just bought my very first car, with some help from my older cousin (A corolla addict) i was able to get a fairly clean '87 GTS Coupe, I am super excited and i got it or a smokin deal

But i am still learning about engines and how everything works together more or less. I dont want to annoy my cousin to much by asking a whole lotta questions. So this seemed like the next best. So well I was just tinkering around with things and getting comfy with the car, i noticed a white reservoir the cap off and empty, I have done a little bit of research and i think its the radiator reservoir. In terms of placement it sits on the left most of the engine bay. If its a problem, What kind of fluid goes in that, just water..?
Thanks in advance for any help or suggestions, Also i put some pictures of my car down below if your curious

<----- Myself on the passenger side with a stupid grin on my face, still wondering if it was a dream?

