Saving seeds preserves biodiversity by protecting heirloom varieties from genetic modification and biotech manipulation
Saving seeds is not especially difficult, but the most common mistake a novice makes is saving seeds from a hybrid. Although the seed may very well produce a plant, there is no way to know what plant it will produce. The careful hand pollination of two or more plants is not reproduced in its' seed. You may get one or the other parent, or some other mutation of the parents.
If you have an heirloom or open pollinated plant you would like to reproduce or share, seed saving is an excellent way to do so quickly and at low cost. And it will ensure that you can replace or add plants that may not be widely available. Seed saving from edibles that need to be replanted each year is a natural of course. But heirloom and open pollinated annuals and perennials can also be perpetuated with saved seeds. And seed saved from your own gardens are already acclimated to your specific growing conditions.
Start with something simple. Some of the very easiest seeds to collect and grow already self seed pretty aggressively. I find that poppy, morning glory and nasturtium in particular produce a bumper crop each year for me so I normally would have no need to collect them. But marigold, zinnia and sunflower (the seeds usually get devoured by birds) do not always seem to produce so many offspring so I do like to collect those seeds.
Basic Steps of Seed Collection:
Collect from your best plants for health, vigor, shape, bloom to produce the best offspring
Watch for blooms to wither while deadheading or at end of season. When they just begin to dry and begin brownng they are ready to harvest for seed.
Use a sharp clean garden shear or pruner to remove flower heads
Dry the flower heads completely by hanging upside down in a cool dry place, on a screen, or even just in a brown paper bag.
Many seeds can be shaken out of the flower head after completely brown and dried. Some seeds need to be coaxed out of a pod or the calyx at the base of the flower head.
Once dried completely the seeds should be stored in an air tight container in a cool dry place.
As you get more experienced at collecting and saving seeds, be sure to research tips about specific flower and vegetables. For example, sunflower seeds and echinacea seeds are so rapidly eaten by birds you need to protect the flower heads from them when they are verging on fading. Cover the flower head with a brown paper lunch sack and secure it with a twist tie at the stem. Rattle the bag periodically. Once you hear seeds start to drop in the bag remove the flower at the base of the stem. Hang upside down to totally complete the drying process. You will also find many tips for collecting and drying vegetable seeds if you search.
Experienced seed collectors will often sift and sort the seeds from debris that is collected. I am not that fussy and will sow seeds and debris into the garden bed since I typically am sowing annuals or biennials. If you are collecting vegetable seeds, you may want more precision of seed placement whether you sow direct in the garden or into seed pots.
Give it a try with a favorite plant, or a favorite neighbor's plant!