There is a product called a First Response Fertility Test for women that is available now, you can purchase this product at any store such as Walgreens, Wal-Mart, CVS, or you can purchase it online.
The FIRST RESPONSE® Fertility Test for Women detects FSH (follicle stimulating hormone), on Day 3 of a woman’s menstrual cycle in order to assess her ovarian reserve, an indicator of fertility. Women who want to assess their ability to conceive may find the results of this test useful.
The test must be done on Day 3 of your cycle. Count the first day of bleeding or spotting as Day 1 of your cycle. A small amount of blood in your urine from your period should not affect the results in any way. You must use your first morning urine. You should not have urinated for at least 4 hours prior to performing the test.
Here's the link for you:
http://www.firstresponse.com/fertilityTest.asp
Are you just generally curious or do you have some reason to suspect it will be difficult in your case? If you have no reason to think otherwise (such as having a congenital problem or an illness that is known to make conception difficult) you probably have as much chance as an average person. If you are about to marry the King of Italy or something and need an heir, you can have blood tests done to check your hormones, and ultrasounds, HSGs and MRIs done to be sure your uterus is in good shape and Fallopian tubes are clear. I wouldn't bother. You are probably fertile, most people are.
If you are asking how do you know in a given month if it is a good time to try to get pregnant, you can take your temperature daily before you move in the morning and watch for an increase, which indicates ovulation (look on the Internet for instructions under temperature and ovulation). Or you can buy ovulation test kits at the drugstore.