The Draw object introduces two components.
As always, create a new compoent with gameObject:AddComponent( "ComponentType"[, params] ).

Check out the function reference for the full list of functions you can use with these components.

Line Renderer

The LineRenderer component allows you to easily create a line in the 3D world.
In addition to the component, you have to setup a model renderer on the game object yourself. The model used for the line should be composed of a single block at a position 0, 0, -8 (in the model editor) with a block size of 16 in all axis.

You can define either the direction and length of the line, either the "end position" (one of the extremities, the other one being at the game object's position).

Circle Renderer

The CircleRenderer component allows you to easily create a circle in the 3D world.
The game object is the center of the circle which is created in the x, y plane.