If I want to make a running animatiion play and fire when a player moves what do i do?

Each character has a set of animations located inside of them. If you want to change the walking animation specifically, you want to change the animation for walking inside the script. You can do it as follows:

game.Players.PlayerAdded:Connect(function(player) --Fires when a player is added

player.CharacterAdded:Connect(function(character) --Fires when the players character is added to the workspace.

character.Animate.walk.WalkAnim.AnimationId = "rbxassetid://".. 92139127218 --Your animation ID

end)

end)