Prepare the food that you wish to preserve. Remember that it needs to be high in acid and below a pH of 4.6. You can test the pH level of the food with a testing strip or pH meter. If the food is just over 4.6, you can raise the acidity by adding some fresh lemon juice.
Wash the jars and the lids thoroughly with very hot water and a mild soap. Rinse the jars and lids, then place them into a clean, soap-free sink filled with hot water to await being filled with the food. To be extra safe, you can boil the jars and the lids in a large pot to sterilize them, removing the jars one at a time with tongs whenever you are ready to fill the jars with the food. You never want to fill hot food preserves into cool glass jars, as it could cause the jars to break.
Remove the jars from the sink or boiling water and place them on a clean towel. Using the funnel when possible to avoid spilling and dripping, fill the jars with the food. If you accidentally drip food on the edge or jar, wipe it up with a clean towel. Leave 1 inch of space at the top of the jar. If you fill the food all the way to the top, you may not be able to successfully achieve a vacuum seal after the jars have been boiled and cooled.
Remove the lids from the hot water with the tongs, place them on the jars and carefully tighten them on the jars.
Place another large pot on your stove burner and put a circular cake rack or the bottom of a spring form pan into the bottom of the pot. This will prevent the jars from touching the bottom of the pan and breaking.
Place the jars into the pot on top of the rack pan bottom. Only put as many jars into the pot as will fit without touching each other.
Fill the pot with hot but not boiling water. Make sure that you continue to fill until the jars are completely submerged and water covers the jars by at least 1 inch.
Turn your stove burner on to medium low and slowly bring the pot to a boil. Keep the water at a gentle boil for as long as your food preserve recipe calls for. Generally, larger jars will require longer boiling times, but make sure that you follow the recipe closely.
Turn off the heat after the jars have boiled for the time required by the recipe, then let the pot and the jars cool down to room temperature.
Push the pop-top button on the lids down. The pop-top lids should stay down when the jars are completely cool. If they don't stay down, you may need to wait longer and try again. If they never stay down, it indicates that the jar is not properly sealed and the food will not be suitable for long-term preservation and storage.