How to get all players in a certain area?

Long story short, I'm creating a minigame type game. I have doors that open up then players walk in. Whats the best way to grab all the players in an area?

To answer your question, all you need to do is grab all of the player's HumanoidRootPart to your position that you want:

function teleportAllPlayers(partToTeleportTo)
	for _,i in pairs(game.Players:GetChildren()) do
		i.Character.HumanoidRootPart.CFrame = CFrame.new(partToTeleportTo.Position)
	end
end

Usage:

teleportAllPlayers(game.Workspace.DemoPart)

I am assuming that you are trying to teleport all of the players in the room. To do this all you need is a Region3. Make it the size of your room. Then when it is time to teleport the players in the room loop through all the players in the game and use an if statement to check and see if they are inside the Region3. You provided no code so I will write none for you. If you have any additional questions just post them in the comments below my question. I hope this helps and have a great day scripting!