A variable is letter or word used to represent a value that can be altered. The main types of variables are bool, string, int, and float. Bool is when the variable can be true or false. String is a letter, word, or phrase. Int is an integer (whole number). Float is a number with a decimal (can also be a whole number).
Examples:
int x = 1; int k = 73; float r = 5; float pi = 3.1415; bool tf = false; bool w = true; string h = "h"; string aa = "lava";
Local and global variables are variables that have a certain scope compared to the script in which it is located in. There are certain levels of scope to a script, there is the function's scope, then there is the local scope, then there is the global scope.
A function's scope consists of everything within its braces ({ }). Normal variables as shown above will only work in a function unless carried over to another function.