A vacuum sealer does pretty much what its name says. It vacuums, and it seals. You have probably seen ads for one famous brand on TV. They are usually used to preserve food, but other items can be preserved as well.
A vacuum is a place with no air. Outer space is a vacuum. The inside of an incandescent light bulb is a vacuum. A vacuum cleaner doesn't actually create a vacuum, but it does move air. Where there is no air, there is no oxygen. Food spoils when it oxydizes, meaning that it combines with oxygen. Take the air away, and the food will last a lot longer. A vacuum sealer takes all the air out of a plastic bag that has some food in it, or something else that you want to preserve.
Once all the air is out, the bag has to be sealed or air will get back in again. A vacuum sealer melts the top of the plastic bag together so the food will be protected. The plastic bags are especially made for this purpose. The wrong kind of plastic bag will just melt all over the sealer and make a mess. The special bags are also strong enough to be put in a microwave or boiled. Many brands of vacuum sealers also come with canisters that can hold a vacuum and be sealed.
Vacuum sealers come in models meant for use in a family kitchen, and larger units used in commercial settings. The main difference in the types of sealers is that some are chamber units and some are non-chamber or external units. Non-chamber units cannot seal liquids. In fact, anything moist such as meat or fish should be frozen before being vacuum sealed. This keeps the moisture from being sucked into the machine. After sealing they can be put back in the freezer, where they will last quite a bit longer than they would in their grocery store packaging. Non-chamber units use a vacuum channel to remove the air from the bag or canister.
Chamber units have a vacuum pump instead of a vacuum channel. The pump is more powerful. This type of vacuum sealer can seal a volume of liquid. It uses a different type of sealing bag than a non-chamber unit. Do not use a non-chamber bag or a bag not meant for vacuum sealing.
Automatic vs Manual
When using a vacuum sealer, read the instructions about when to use the Automatic function versus the Manual. Automatic switches between vacuuming and sealing by itself. On manual, you have to time when the vacuuming is done and the sealing should begin.
A vacuum sealer can save money by saving food. It also can keep jewelry, silver flatware, and other items from tarnishing. Make sure that no sharp points poke holes in the bag, or the air won't be sealed out. It is helpful to learn tips about how to prepare foods before sealing. For instance, fresh vegetables should be blanched before beiing sealed. All sealed food should still be refrigerated or frozen.