The 25-cent tour ....
The "FoodSaver" is a trademark of Tilia, Inc. (and generally considered to be the best brand around). Deni, Rival, Black & Decker, and some others, also make vacuum food sealers that are "basically" the same thing but are not generally considered to be as good (lower vacuum).
"DANCE WITH THE ONE THAT BRUNG YA": Each brand is a little different, the amount of vacuum it draws, the sealing temp, etc. They all have bags designed to be used in their machines - don't try to mix-n-match. That's according to my son that has tried different brands of bags on his gizmo.
They all work on the same principle - to remove as much air as possible. This does two things ... it removes the air that causes meat to oxidize (what happens when it turns brown) and form ice crystals, and it makes food last longer because it removes the air that enzymes, molds, etc. need to cause the food to go bad.
To use - follow the instructions that come with your vacuum gizmo. Personally, when I get something like a hunk of cow ... I remove it from the original "plastic tray", blot it try with paper towels, then bag it. What once used to go "yucky" now looks pristine, and taste good too, up to about a year.
"It ain't what you don't know that gets you in trouble. It's what you know for sure that just ain't so." - Mark Twain