BBT confusion

Alexandria • Two angel babies👼🏻👼🏻 Avery 5/31/20👶❤ planning for #2👶

Im very new to ttc and i keep hearing about bbt(i know it stands for something to do with body temp) and i was just wondering if anyone would be able to explain it to me and how to record it. What ive read so far has me confused 🤦🏻‍♀️

Thanks in advance ladies!!