I highly recommend reading "Taking Charge of your Fertility". You can choose to read only the chapters that relate to you, but you will find all of the details and what everything means, which is helpful because every body is different.
Essentially, you take your temp before getting out of bed every morning. It should be about the same time. When you keep track of it, you see that it is lower before you ovulate than after. Understanding your cycle can help you time bd and recognize any potential problems with fertility. You should also watch for cm, as it is another indicator that will give more info about ovulation.
Another note... If you can find a basal thermometer that uses Fahrenheit, the readings will be a little more detailed. I started with a Celsius one, but had a much easier time once I switched.