There are lots of ways to get seeds. If you’re lucky you’ve got some good weed with seeds already. Clean the weed and harvest the seeds. That’s pretty simple, except that most weed these days comes without seeds. In fact, it’s been that way so long that it’s not even called “sin semilla”, which was what we called it in the old days before growing only females was common .
You can always buy seeds. In some areas there are stores that sell them over the counter. You can also get them online or through magazines. Buying seeds gives you much greater choice. Be careful, though- buying or selling seeds may be illegal in your area.
Regardless of how you do it, you have to get some seeds.
Different strains of weed produce different strains of seeds. Some are fat, round balls. Others are little. Some are dark. Some are light. They can come spotted and dotted. They can have stripes or look camouflaged.
That isn’t important. The husks should be hard and should not crush easily (don’t try hard to crush them – you can crush good seeds with your fingernails).
If they’re small, soft, easy to crush and bright green, they’re too young.