This guide is going to go over both how to get toasts and how to use them
How to use them: Finish a match of any mode and after each team has decided to rematch or not if the mode allows rematches, it will have an icon appear each of the players heads that says "Give Toast" and you can hover your cursor over it and press A or X for PlayStation Controllers to give the toast as long as you have them
Tips: Play either free for all or teams so that you can give 3 toasts each game as long as you have them
Bonus tip: Have a friend that you are matchmaking with so that you can also make progress on the playing in a party 500 times achievement
How to get toasts: The game automatically starts you with some
(Not 100% sure on this one) - Doing the tutorial will give you toasts, if not, I do know it gives wonder woman.
Each day new characters come into rotation, always try to get these characters to level 3 by playing public matches. Each character once hitting level 3 will give you 5 bonus toasts
Leveling up the battle pass
Whenever you are able to toast you can click at the top right where it says to buy more toasts. You can do this with gold and is my last resort method.
Follow this and at 100 toasts you will have your final toasting achievement.