You can get seeds many ways. If you’re lucky you’ve got some good weed with seeds already. Clean the weed and harvest the seeds. Unfortunately, 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 buy seeds, of course. In some jurisdictions it’s legal to sell them openly. You can also get them online or through magazines. Purchasing seeds from a seed dealer allows for more choice and great quality. 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.
Seeds differ widely with the type of pot they come from. Some are big and fat. They can also be tiny. They can be very dark. They can come with light coloration. They can come spotted and dotted. Some have tiger stripes or blotches.
What is important is that they are genetically mature seeds. 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 are soft and green they’re too young.
Get an idea of how marijuana is growing.
Learn the tips how do you grow marijuana.