Hello Olivia,
Start at the beginning, make sure when you thread the machiune that the presser foot is up, make sure the needle is in the correct way round, top tension about 4 or 5, use a good mercerised thread other thread will have flaws and cause tension problems, you should be able to pull the bobbin thread through with some slight resistence only and make sure the bobbin turns anti clockwise in the bobbin case.
ken
drivewithken@blueyonder.co.uk, January 2009