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You can either use fresh lemon juice, or lemon juice from a bottle. The lemon juice will be added to the jar along with the tomatoes. The juice helps to prevent the tomatoes from spoiling while they are in the jars, and also helps to retain the color and flavor of the tomatoes. Place the jars on a heat resistant surface and begin spooning the quartered tomatoes into the jars. Fill the jars until there is only about ½ of an inch of space left at the top of the jars. Add two tablespoons of lemon juice. You should also add either boiling water or hot tomato juice so that the jar is filled up to ½ an inch away from the top. You could also consider adding other ingredients to enhance the flavor of the tomatoes. Cloves of garlic, peppers, or a sprig of basil make delicious additions to canned tomatoes. Once you have added the lemon juice, gently press on the tomatoes with a spoon to release air bubbles. Air bubbles are bad because they can let bacteria get into the jars, thus spoiling your canned tomatoes. You should also slide a sterilized knife or plastic spoon along the inside wall of the jar, releasing any air trapped there. Place a lid on top of the jar and screw on the band with your hands.
Choose your lemon juice. Fill the jars with the tomatoes. Remove any air. Wipe away any drips along the top and sides of the jar.