it takes the average healthy couple up to a year to conceive.
you need to have sex when you're ovulating. to know when you're ovulating you need to keep track of your cycle, day 1 of your cycle is day 1 of your period. you ovulate 14 days *before* your period, most women have a 28 day cycle, so they ovulate on day 14. in this case you should have sex on day 10, 12, and 14.
even if you have sex at exactly the right time, there's only a 25% chance of conceiving.
not every woman is the same and nobody knows *exactly* when they ovulate, so if you're not trying to conceive you should always use some form of protection. if you are trying to conceive, you need to pay attention to your body.