There are three major sections in threading a sewing machine.
1. Winding the bobbin: place your thread spool in such a way that the spool pin on the machine is inserted into it. Pull the thread out of the spool and thread the bobbin. Place your bobbin on its pin and start the bobbin winder. Remove the bobbin after you must have finished winding it.
2. To thread the upper half of the machine: place your thread spool back on the spool pin, and wrap the thread strand around the thread guide. Pull your thread down and wrap it around the take-up lever. Take it some lengths further to thread your needle.
3. To thread the lower half of your machine: Remove the cover on the lower compartment. Unwind a few lengths of thread from your bobbin, and place it below the needle in the compartment. Turn the wheel of your machine with your hand to bring out the threaded needle. Now, you have successfully threaded your sewing machine.