What is the exact science behind getting pregnant?

I know i might seem dum but im alittle confused as to how we get pregnant. i know that you can be most fertile when the egg drops (i think) and that is 24-36 hours and the best time to try and conceive. so how do we get pregnant without the egg there? i know the eggs come from the ovaries but how do you get pregnant when your not ovulating? its there a science website i can look at with diagrams etc? thanks.