There are other parts of the forums you should read up on, but ill give you a cheat sheet..
Pic 1 is male sacks
Pic 2 is female pistils

Males usually show their colors first before females do.. if its a boy there will be little pods filling up at the upper internodes, with a microscope they look like litttle seed pods.
Females show white pistils that crop out amongst the internodes as well, easily distinguishable..