Saving tomato seeds is easy. Allow fruits to ripen fully and scoop out the seeds, along with the gel surrounding them, before you eat or cook the tomatoes.
Rinse your tomatoes and slice. Squeeze out the seeds from the flesh. Put the seeds and gel in a glass jar with some water. Make sure you label the jars for the variety of the seed you're saving.
Stir or swirl the mixture about twice a day. After a few days it will begin to ferment. The fermentation will dissolve the gel covering the seeds. The seeds should sink to the bottom within five days. Pour off the liquid, rinse the seeds in a strainer.
Spread them out to dry on paper towels.
Allow the seeds to dry throughly, store and label, date and store in a paper envelope.