How do you put a bobbin in a elna so i can use it to sew

Drop in a full bobbin with the holes side upwards (I'm assuming this is a Swiss Elna sewing Machine horizontal bobbin design as you haven't given the model number).

Now, hold the thread tail with your right hand and pulll the thread clockwise towards you while holding the bobbin still with a finger from your left hand. Bring the thread tail around towards you until it goes into the little slot, then press downwards onto the thread tail close to the bobbin until you hear it click into the tension spring. Test by lifting the thread tail upwards, it should stay in tension and not come back out of the groove.

Now close the back slide cover over the bobbin leaving the bobbin thread tail visible out to the right.

Now manually turn the flywheel towards you while holding the top thread tail and take the needle down into the bobbin holder area and back to the top, pull the thread tail to bring the bobbin thread up to the top.

There is a threading up diagrams at www.sewusa.com http://www.sewusa.com/Threading_Diagrams/Threading_Pages/Elna_Sewing_machine_threading/Elna_Supermatic_threading_diagram.htm
for the old Supermatic but the bobbin holder design is almost identical for all the subsequent models such as the SU, TSP, Supermatic or Air Electronics like the Stella, Carina or Jubilee, the above is the same for all.