that's a nice machine, one of the last mechanical Elnas with the discs for extra stitches. Firstly, you need to wind a bobbin, always use Elna swiss metal bobbins, with holes on one side only, slightly dished. Put on top of the bobbin spindle and take the thread from your spool on the spool holders at the back of the machine across to the tension disc on top left, its white bump, thread through the tension then back to the bobbin and pull the tail through a hole in the top of the bobbin. Flick bobbin across to the right against the stop, disengage the clutch by holding the outer flywheel and turning the inner towards you. Now press the foot pedal to start winding a bobbin, holding the thread tail so it starts off. Wind one full coverage of the bobbin so that the starting point is covered, then stop and cut the tail off with scissors. Now continue winding at 3/4 speed until bobbin is full, watch as it winds and give the thread a nudge with your finger so it fills top and bottom as well as in the middle of the bobbin. When it is full, the bobbin spindle will stop winding. Move it to the left, cut the thread and reennage the clutch by holding flywheel and turning the inner the other way. Now install the bobbin and click the thread into the tension device, see image.
Now thread up the top thread by taking the top thread from the spool, through the tension discs, across to the eyelet on top, down to the check spring, back up to the take up lever, then down to the needle catching the thread into the two thread guides enroute.
See this image.
Now thread through the needle front to back, hold the top thread, close the bobbin cover leaving the tail sticking out the top, lower the needle down by turning the flywheel towards you through one cycle and pull the top thread, drawing the bobbin thread up to the top of the needle plate with it. Pull both threads under the pressure foot to the back and your ready to go. Remember, top tension should be on 5 and bottom tension should be on the red 1, don't change it. Brush out the bobbin holder assembly each time you use this machine and add one drop of oil into the middle of the bobbin holder, there may be a red dot or just the indenation. Run the machine for 30 seconds after oiling without thread, slowly to spread the oil through the bobbin mechanism. Standard 130/704H needles, change regularly (6 hours of sewing) and pick right sized needle and type point for the work you are sewing. Good luck with your SU. If you wanted to join, there is a Yahoo group called "Elna Heirlooms" for fellow Swiss Elna owners.