How to save data and where to put this script

Hello! I have 2 questions for you guys,

  1. How do I save and access user data?
  2. I am making a training game, how do I make sure that one players stats don’t get mixed into another players stats?

Let me go into more detail because question 2 doesn’t really make much sense.
I have a script with lots of variables like strength, durability, speed etc. But how do I make this script apply to a single player so that everyone’s stats don’t added into the same script.

Hey I just recently answered to similiar question: