Hi,
A couple of tips for vacuum packing.
Vacuum sealers usually have two functions - vacuum air removal and heat sealing.
[see pic bottom] When the lid is up, at the front you can see the heat iron strip. This carries out the heat sealing by pressing both sides of the plastic film together and melting them. Behind that, you can see the foam vacuum loop. When you place an open side to a bag in this loop and close the lid, air is sucked out of the bag before the heat iron is activated to seal the vacuum.
You can make bags to your required size by cutting to size and sealing (all but one of) the open sides using the heat iron alone.
The plastic itself has, obviously, two sheets. One sheet is smooth, but the other sheet has tiny channels that run in a diagonal grid pattern. It is through these channels that air is sucked out of the bag before the heat iron then melts these channels and welds the two sheets together, forming a welded seal.
When preparing liquids, sauces with a high liquid content or fresh meat, it's better to freeze first, as this stops liquid getting into the channels, which could stop a proper seal being formed.
Another thing I've learned is that if you wish to pack fine powders (like milk powder into portions), it's better to wrap the powder in cling film first so the powder doesn't get into the channels.
Steve