About dialing in..

Gooday everyone! So I’m fairly new to the coffee space, and was wondering about how the different variables affect coffee. I did some digging on my own and learnt to control brew time, temp, grind size, flow speeds, etc. But all these factors got me thinking, what’s the difference between adjusting these things. If I have a bitter cup do I go coarser, lower temperature or pour gently? They seem to have such similar effects that I don’t know when to change what ㅠㅠ pls help.