Here is a great recipe for preserving green tomatoes.
Small green firm tomatoes
6 stalks celery, cut in 2-inch lengths
6 sweet green peppers, quartered
6 cloves garlic
2 quarts water
1 quart distilled white vinegar (5%)
1 cup canning salt
Fresh dill to taste
Wash and drain vegetables. Pack tomatoes in hot jars. Add to each quart jar, 1 clove of garlic, 1 stalk of celery and 1 green pepper cut in fourths. Combine water, vinegar and salt. Boil with the dill for 5 minutes. Pour the hot brine over the pickles in jar, leaving ½-inch headspace. Remove air bubbles. Wipe jar rims. Adjust lids. Process 15 minutes in a boiling water bath. These will be ready for use in 4 to 6 weeks.
Source: So Easy to Preserve, Cooperative Extension the University of Georgia.
The process for “boiling bath canning” involves placing loaded jars with lids finger tight on a rack to keep them off the bottom of the pot they are in. You’ll want to submerge the canning jars in hot water, (about the temperature of the water in the jars when placed into the canning pot). Fill the pot to 2 inches above the jars. Bring the water to a boil, then start counting time for the 15 minutes. Let the Jars sit a few minutes after the time is complete with the fire off. Then lift them straight up and transfer to a draft-free place and allow them to sit for 24 hours. Store in a cool, dry place for the 4 to 6 weeks it will take for them to become delicious.