How do I focus the camera?

game.Workspace.CurrentCamera.CameraType = Enum.CameraType.Scriptable -- You could use Fixed, but you might still want to move the camera.
game:GetService("RunService").RenderStepped:connect(function()
    game.Workspace.CurrentCamera.CoordinateFrame = CFrame.new(10,50,30) -- You can use a variable if, for example, you want to zoom in or out.
3
    game.Workspace.CurrentCamera.Focus = CFrame.new(0,10,0)
end)

You want to use Coordinate frame , it has two parameters:

It can set a position for the camera

It can set what the camera is facing

More detailed explaination:

CoordinateFrame:

First of all, CoordinateFrame is the extended name of CFrame. The CoordinateFrame property of the camera is simply the position of the camera.

game.Workspace.CurrentCamera.CoordinateFrame = CFrame.new(10,50,30) 
-- Positions camera at 10, 50, 30

Focus:

The Focus property is simply that the camera is looking at. To set the Focus property, you would do it the same was as CoordinateFrame:

game.Workspace.CurrentCamera.Focus = CFrame.new(0,10,0) 
-- Makes the camera look at 0, 10, 0

Setting the Focus will automatically rotate the camera in it's CoordinateFrame position.

Locking the camera:

Sadly, setting these properties does not lock the camera's position. The player can still rotate and move the camera around at their will. Currently there is no efficient way to go about solving this, that I know of. For now, the only way to lock the camera is to set a continuous loop. Example:

while true do
    game.Workspace.CurrentCamera.CoordinateFrame = CFrame.new(10,50,30)
    game.Workspace.CurrentCamera.Focus = CFrame.new(0,10,0)
    wait()
end