I don't know how can a woman know if she is fertile or not?? I want to know it for my own good... thank you... :)

Do you mean, you want to know if you are ovulating? If so, there are tests similar to those of pregnancy tests that can tell you.

If you want to know if you are fertile, you can go to the doctor and they can tell you.

Do you track your cycles? A common method, though not the only one, is based on this... but it means you need to keep accurate info on your cycles.

Also you can track using basal temp or cervical mucus.

Some would recommend using more than one means for best results.

All methods take work on your part. Also, understand that none are perfect means of birth control, if that's what you are looking for... not sure if you are wanting to get pregnant or looking to avoid it.

Simply Google or Yahoo something like "how to determine when fertile" and you'll get some hits most likely.

The only catch is if you have sex without the man using a condom, the sperm can survive for a time within the woman... so a person might think she's "safe" when she's not.

Determining ovulation takes time and skill. Use the book Taking Charge of Your Fertility and/or the website FertilityFriend to help you. This involves taking Basal Body Tempratures and observing cervical mucus as well as (optionally) cervix observations.