This becomes useful information for interpreting mucus changes which are the most important bodily change during the menstrual cycle as far as fertility is concerned. It is the job of the cervical mucus to either restrict or allow sperm penetration through the cervix. It helps you decide if you are fertile or not. It is easy to imagine that mucus that is dry and thick is not as easy to swim through than mucus that is wet and slippery. Different women have different symptoms or charateristics of mucus, differences in the wetness, colour, smell, pastiness, so only you can know what your own personal pattern is.
Personal observation is vital.
Observing mucus is simple. We are only interested in the mucus that is readily observable at the mouth of the vagina. You need only touch the mouth of the vagina or alternatively wipe vaginal mouth with a tissue and feel mucus from that. Physically charting your observations on a calendar or diary speeds up the learning time considerably. The section Keeping Track goes into this in more detail.