What is the difference between jing and qi ?

im asking cause im confused a bit about it  -  i used to hear that jing is something you have from birth and you should try to preserve it and when you get old you are slowly loosing jing 

yet recently i asked here how to not get wet dreams (if i dont want to have sex or masturbate)  and got an advice to turn jing to qi (if someone wants to add an explanation how i do that - can be nice)   ....   so by what i heared in the past it seems like a bad idea to turn jing into qi ... and if anything it should be the other way around ...

would love to hear whatever info people can add on the subject of jing vs qi