Advantage does have everything to do with rerolling in 5e, but what I'm understanding from you guys is that for some reason this was never part of the dice rolling process players can do in the game.
I feel hoodwinked. They definitely need to change this.
Advantage and re-rolling are quite different things in 5E, as explained by mrfuji3. The fact that you have them confused is exactly why Larian needs to explain these concepts better.
There are cases where you can roll with advantage/disadvantage AND do a re-roll, which is why this needs to be cleared up.
I see what's happening here. I am using reroll in the literal sense of the action, not in the sense meant to explain how Advantage/Disadvantage works, that's my bad and I can see why you would think I believe that. In my D&D game I just have 1d20 to roll, so when I have Advantage/Disadvantage I have to reroll the same dice to get the other number. In this game, we have 1d20 on the screen, so iIf we have Advantage/Disadvantage, we should be able to use the Reroll button in order to get the second number. If Larian wants to get fancy, then maybe in a future update they will have two d20s on the screen when you have Advantage/Disadvantage.