How do you tell difference between male and female marijuana plants?

the first flowers appear where the leaf connects to the stem. the female has a bulb shaped structure. the male flowers appear to look like a small light green cluster, kinda like grapes

male plants are smaller, thinner, seedier, have smaller leaves (overall they suck). The females on the other hand are bigger, thicker, grow bigger leaves (those are the ones you want)

Female plants do not have seeds

males have balls not buds

No, you cannot tell from the seeds. You will only be able to tell when the plants reach the flowering stage. Male plants will produce pollen sacks.