How do I make a slide door with two sides?

I may suggest that you use a touched event w/ invisible bricks to detect when to open the door. Then once you know when to open the door, you can use a for loop to change the door's CFrame, here is a little example.

door.Touched:connect(function(hit)--touched even
    if hit.Parent.Humanoid ~=nil then--detecting if the part that touched belongs to a player
        for i=1,100 do--for loop, it will run 100 times.
            door.CFrame=door.CFrame + Vector3.new(0, 0, 0.1)--editing the door's CFrame
            wait(0.1)--waiting...
        end
    end
end)