can someone tell me how this thing works?

i don't understand how it sucks paint up... or whatever it does with paint so it comes up that straw...
it's brand new and everything is clean and works but i can't get paint out... it just blows air... i tried blowing air with my mouth threw paint nozzle and it's all good and clean... so what should i do? i don't even understand why would paint come out of that jar all by it self...