If this season you have grow a type of tomato that you like a lot…. then seve its seeds for next season. The main thing is that it isn’t F1 hybrid.
This because its reproduction doesn’t assure you the same plant but one with the ancestor features.
Choose one tomato, cut in half, pick up seeds, put them in a jar with water (about 1:2 as proportion), wait two or three days that a little layer of milldew grows, remove it away, recover your seeds, wash them well, put them to dry on a paper towel and then storage them in a paper bag for next seeding.
All this operation is to elimainate the jelly-like skin that cover seeds and that avoids their germination.
As soon as possible I put the photos of the making of. Stay tuned.