How to use UpdateASync properly?

Sometimes reading the Wiki can be painful... I understand!

Okay, for your question...

UpdateAsync is a method for storing a Player's data in DataStoreService.

There are 2 parameters you must mention when using UpdateAsync. The key for the player's entry (Key) and a function that returns the updated value for the key.

Let me show you an example:

local ds = game:GetService("DataStoreService"):GetDataStore("PlayeData") -- Name the DataStore whenever you like!
game.Players.PlayerRemoving:Connect(function(plr)
	local key = "plr-"..plr.UserId -- Use UserId instead of the player's name because the player's name may change overtime!
	ds:UpdateAsync(key, function(oldvalue) -- Imagine the value is a number...
		local newvalue = oldvalue + 100 or 10 -- just to make sure that oldvalue isn't new, or else just treat it as 10.
		return newvalue -- Returns and updates the value!
	end)
end

To be honest, using UpdateAsync is useful if the old values may be important! If you don't want the old values, use SetAsync which directly uses the value as the second parameter instead of a function!

For example (in one of the many lines in the script), ds:SetAsync(key, 500). This directly sets the value to 500. Of course, that would be kind of ridiculous!

That's all I can tell you. If you have anymore questions, please ask me in the comments below. Thank you and I hope this will help you!