At the point the plant starts producing pre-flowers. I can tell if they are males based on them having more bell shaped formations. But with females you get more long stringy appendages.
Source: https://www.growbarato.net/blog/en/how-to-sex-marijuana-plants/
There we can see how they look different.
Once I grow the buds I will harvest them, dry them and then cure them. Which takes around three months in time. After that I can smoke them, vape them or cook with them. I can make a really strong canna-butter with the buds or even from the trimmings.