please some help

i want 2 start from seeds but what i dont get is when do thay start to show if thay are male and female do i flower too find this out then clone then put the clones back in 2 veg plz help thanks

there's no way really sex before flowering. they will start to show pre flowers once they reach sexual maturity (which could be anywhere from 6-8 weeks veg. time depending on a lot of factors), which is the appropriate time to start the flowering stage. you should take clones before flowering and make a note of which plant the respective clones came from. once the plants show sex, you can kill the males and eliminate the clones taken from them, leaving you with only females and female clones.
flowering them early until they show sex and reverting back to veg will only stress the plant and most likely make it turn hermie. just be patient and wait for those pre-flowers.