When your cervical fluid is slippery and stretchy your fertile window is open and you will likely ovulate soon.
After ovulation, your estrogen levels will drop and your cervical fluid will be drier and less fertile.
After ovulation your body produces progesterone which increases your waking oral temperature.
Your egg only lives for up to 24 hours, so by the time you see your temperature rise, your fertile window has closed.
Temperature is helpful to confirm you are ovulating, timing intercourse correctly, and have a healthy cycle that could support a pregnancy.