The first step is to cut the tomato into two halves. Then rub the two halves against each other above a bowl, so that the seeds and the pulp will be loosened from the skin of the tomato. Now you have two options for further proceeding.
The first one is to pick the seeds from the pulp, put them on a kitchen paper and let them dry. If you plant these seeds in your garden, it might take some time before they begin to germ. The reason for this is the outer layer of the seeds which hinders quick germination. This layer needs to be removed by the plant itself before germination.
Another option is that you remove this layer which hinders germination. This can be done by putting the seeds with the pulp into a glass and fill it up with water. The glass should be placed at a warm place for three days. Please stir the liquid in the glass once a day. Be careful that you do not exceed the recommended time of three days, otherwise the seeds will begin to germ. After this fermentation process you sieve the liquid, put some fresh water into the glass and shake it carefully. This helps that the seeds get rid of the remaining pulp. The procedure should be repeated until the water stays clear. As the last step you put the clean seeds on a kitchen paper and let them dry. If you plant these seeds into soil, you will see that the germination process will occur promptly because there is no layer which hinders germination.
For storage you put the seeds into a glass with twist-off lid. If you have seeds from different tomato varieties, we recommend to mark each single glass accordingly. You can store the glasses at a dark and cool place. This way, the tomato seeds will stay germinable for about eight years.