Steam Canner/Water Bath - Jams and fruits and acid foods such as tomatoes, pickles, pickled foods, relishes do not need to be canned in a pressure canner. Water bath will do the job. Water bath and steam canner raise the temperature up to 212 degrees. The timing required is a function of how well the contents conduct heat so the inside of the container gets to 212 degrees and how big is the container. Both accomplish two things:
Raises the temperature in the contents high enough to kill bacteria, molds and yeasts and forces out the air to create a vacuum to make the jar seal.

Pressure Canner - Low acid vegetables require higher temperatures (240 degrees) in oder to kill botulism caused toxins. You can only get them to 240 degrees by the use of pressure canner. The timing required is a function of how well the contents conduct heat and how big is the container. That is why quarts need longer time than pints. The pressure canner accomplishes two things: Raises the temperature in the contents high enough (240 degrees) to kill toxins created by certain bacteria such as botulism and forces out the air to create a vacuum to make the jar seal.