What Service or type of script is used to make a "part" appear behind your character when he walks?

Im thinking about making a game that makes it to where when you walk a part appears behind your character such as in murder mystery

I would recommend that you have a LocalScript in every player that makes it so that every 5 or so seconds, a small part is made where their feet are, and then 25 seconds later, the part is destroyed.

Example:

wait();
script:destroy();--// Anti Death Removal

local Player=game:service'Players'.localPlayer;
local TrailSize=2;--// The trail size. Can be changed.

while(wait(5))do--// Do this every 5 seconds
	local Character=Player.Character;

	if(
		Character--// If they have a character
		and Character.Parent=workspace--// If the character is in the workspace ( prevents errors from falling off the base )
		and Character:findFirstChild'Right Leg'--// If they have a right leg
		and Character:findFirstChild'Left Leg'--// If they have a left leg
		and Character:findFirstChild'Humanoid'--// If they are a real character
		and Character.Humanoid.Health>0--// If they are alive
		and Character:findFirstChild'Torso';--// If they have a torso
		and Vector3.new(
			Character.Torso.Velocity.X,
			0,
			Character.Torso.Velocity.Z
		).magnitude>=2--// If they are walking
	)then
	
		local Trail=Instance.new('Part',workspace);--// Create the trail part
		Trail.Name='Trail: '..Player.Name;
		Trail.formFactor=3;
		Trail.CanCollide=false;
		Trail.Anchored=true;
		Trail.BrickColor=ChatColor.Get(Player.Name);--// *****
		Trail.TopSurface,Trail.BottomSurface=0,0;
		Trail.Size=Vector3.new(TrailSize,TrailSize/2,TrailSize);--// You can change this to represent the trail size.
		Trail.CFrame=
			CFrame.new(
				Vector3.new().lerp(
					Character['Right Leg'].CFrame.p,
					Character['Left Leg'].CFrame.p,
					.5
				),
				Character.Torso.CFrame.p--// Where the player's character is facing.
			)
			* CFrame.new(
				0,
				-Character['Right Leg'].CFrame.Y/2,--// In between the player's feet.
				-2 --// A little bit back.
			);

		game:service'Debris':addItem(Trail,25);--// Removes the trail part after 25 seconds

	end;
end;

***** Interesting ChatColor class found on NoliCAIKS' code snippet container. It gets the Player's chat color, which is determined by their name.

Oh! That is called pathfinding! Go to this link!

http://wiki.roblox.com/index.php?title=Pathfinding