Susan,
If you have the 'sealer top' that fits over the mason jar....fill the jar and leave about 1/2 to 1 inch of space. Make sure the top of the jar is clean. Make sure the 'rubber' on the thin metal lid is clean too. Seat the thin metal lid onto the jar and place the 'sealer top' over the metal lid and 'press' down (until it feels as if it is seated completely). Attach the tube from the sealer to the top and turn it on. (For my machine...)When the vaccuum is complete, the machine turns off the suction (Idon't know if it will for yours). Remove the 'sealer top' and place one of the mason jar 'metal rings' over the vaccuum sealed metal lid. All should be complete. If you find that after turning on the machine, you don't seem to have any vaccuum sealing occurring but it is obviously attempting to apply suction.......try to "screw" the vaccuum sealing top down while the suction is on. This will help to seat the metal lid better.

Hope this helps.