Generation (a) or (a, b, c)

I can’t figure out how my credits get used up? So, if I write three queries:

red dog
red dog with bushy tail
cartoon red dog with bushy tail in the sun

…is that three CREDITS used? Or, am I only deducted a credit when I download?

If the former - is there any way to ECONOMIZE within queries? So, that small, incremental changes don’t use credits?