This lesson asssumes you have some experience with Logo. You should know all the commands listed below, and feel comfortable in the Logo program.
HOME moves the turtle to the center or origin of the drawing window.
Sets the turtle heading to 0 - makes it point to the top of the screen. A Procedure is just a collection of Logo commands that performs a specific task. Thus, BACK is a procedure that tells the turtle how to move backwards. You can teach it how to do specific things - draw a square, for example. You are going to draw a square with sides that are 50 turtle steps or pixels long.