How i can create a Combo?

First things first, I recommend reading about Animation Events because it can easily be one of the best ways to do this: GetMarkerReachedSignal

And one thing you should know is tick(). now tick() is a time function that's local and very inconsistent (use os.time() if you want an actual good, global time measurement) but for the sake of this example tick() will work perfectly.

Now you can use tick() to do something like this:

start = tick()
timeInSeconds = 3

while (tick() - start) >= timeInSeconds do
	-- this code will **ONLY** run when 3 seconds have passed since start has been updated
	wait()
end

-- and maybe something like this
while (tick() - start) <= timeInSeconds do
	-- this code will **ONLY** run as long as 3 seconds have passed since start has been updated
	-- now obv this code will not run because of the above code but you get the idea
	wait()
end

You see where I am going? Using this way we can see whether or not the player has pressed at a decent time (eg. 0.01/0.2)

Now I am no expert in this nor did I try doing this but let me try, alright?

We will start with input, you will have to listen to when the player presses (and keep track of it) which you are doing rn. And we have to keep track of when the player first pressed. so it will be similar to this:

playingAnim = false
timeOfPlay = nil

LCD = 0.01 -- LEAST_COMBO_DELAY
MCD = 0.2 -- MAX_COMBO_DELAY

function startPlaying()
	playingAnim = true
	timeOfPlay = tick() -- we are recording this to have a good measure of time
end


function press()
	if not playingAnim then -- if this condition passes then the player is trying to hit their first hit (no combo whatsoever)
		startPlaying()
	else -- if this condition passes then the player is trying to hit again while the first animation is playing (in other words, they want to start a combo)
		if (tick() - timeOfPlay) >= LCD then -- recall when we stored timeOfPlay? this means that 0.01 secs have passed
			if (tick() - timeOfPlay) <= MCD then -- this means that the time passed is less than (or =) to the MAX time (0.2)
				-- here we will repeat the same process with each applicable hit, make sure the player can't make a combo with 300 hits though lol
				-- now remember when I asked you to read that animation thing, you should use it here, only if you want a smooth and cool transition (and probably no lag too)
			animTrack:GetKeyframeReachedSignal("ComboCanBePlayedHere"):Wait()
				-- make sure to add the part that can be transitioned from and call it whatever you want but make sure to change it here too
			end
		end
	end
end