Think of VAR as a high school algebra equivalent of "X" where it's value can change and isn't a set number.
So, if Var + 2 = Var2, then that would be like x + 2 = y.
Here's an example:
Var [MaxHP] = 10
// (the max health points equals 10)
Var [HP] = [history:Lvl] + 2
// (the player's current HP count is whatever level they are, +2 (sets level 1 to 3 hearts))
IsVar [HP] > [MaxHp]
Var [HP] = [MaxHp]
// (do nothing)
What that does, is set your max HP to 10 and your HP cannot go above 10.
Note: This does not actually work, it's just an example for var.