Daffodils and crocus are all classed as spring bulbs even though crocus is technically a corm not a bulb. The difference is like the difference between a head of garlic and an onion. Both grow daughter segments around the mother bulb and when there are a lot of smaller segments the energy of the plant is diverted to support that development rather than produce a flower. The result is that green leaves come up as normal in spring, but very few flowers are put out. The remedy is to divide the bulb and space them out so that they flower again next year.
In daffodils and tulips, which are true bulbs, the offsets are grown around the main bulb and the new shoots emerge vertically from that segment alongside the parent shoot. As the years progress, the offsets completely surround the mother bulb.
In corms, the cormels form around the base of the mother corm. Each little pea shaped cormel stays attached to the main corm while it matures and grows. The cormels eventually separate from the parent.
To divide the bulbs and corms, wait until the green leaves have started to turn brown and then cut the decaying leaves off. Dig the bulbs up and rinse carefully. The offsets and cormels are usually apparent and some segments will drop off when you lift the bulb. Others can easily be pulled off with your fingers leaving a single bulb again, and lots of smaller bulbs. Replant the bulbs in new places in the garden and by next year all but the smallest segments will grow and flower for you.
It is not necessary to wait until the whole mass of bulbs are so overgrown that they show declining flowers and most bulbs benefit from being divided every three to five years just as your other perennials do. Of course if you have an especially beautiful daffodil that you want to share with your friend, you can do that too once the bulb is mature and has a few offsets or cormels set.
Examples of true bulbs are daffodils, tulips and ornamental alliums;
Examples of corms include crocus and gladiolus.