When threading a machine, it is important for the thread to go from the spool through the tension plates, over the lift arm, and through the needle. The machine's guides ensure the thread follows the correct path. Every machine is different. Check the owner's manual for your machine's specific steps.
From the back of the machine, pull the thread off the spool and through guide #1.
From the front, pull the thread over the tension plates on the top of the machine.
Pull the thread up through guide #2
Pull the thread over the take up lever.
Feed the thread through guide #3.
Feed the thread through guide #4 just above the needle.