If the vacuum sealer is challenging to remove after sealing the jar, rub a tiny bit of vegetable oil inside the sealer on the rubber part that contacts the Mason jar.
Also, don’t push the sealer down quite so much. When you press the “start” button, you should hear the noise start to change pitch. If it doesn’t, push the sealer down a bit snugger. You’ll get it after a few tries.

It depends on the size of the jar and how full it is. Listen for the pitch of the machine to change. After that, I usually run it for about 10 seconds to get a tighter seal.

First, push the sealer down with slightly more pressure. If that doesn’t help, check to see if something is keeping the jar from sealing. Most likely, there is a particle of some food between the edge of the glass opening and the flat metal lid. Remove the sealer and make sure the top edge of the jar is free of any foreign objects before trying again. Occasionally, there can be a small chip or malformation in the jar that causes a problem. Move to the next jar.