Checking your temperature to monitor your cycle is frequently called "charting" your cycle. You do this by checking your temperature every morning as soon as your rise, before you get out of bed. This is known as your Basal Body Temperature.
As you go through your cycle your temperature will have slight shifts. Once ovulation occurs it will shift again. In order to have any predictability you need to chart for about 3 months to get a baseline for your body. One thing charting can help with is to identify if you have any other potential hormonal issues and to confirm that ovulation is occurring.