BBT newbie

Hi guys

So I haven’t done a lot of bbt charting ; I’m not sure how I would do it

Can someone explain how it works and how should I start doing it for next month ?

for this past week I’ve been checking my bbt through my mouth every other morning around the same time to get use to it , and it is my DPO week ;

This week it’s always at high 97- and low 98.83 F

And today I checked it which is a day before AF should show up and it was low 97F

I’m sure I’m doing this wrong

But I was wondering if this week bbt should matter ?

If I got a low temp today does it mean Im out for the month ?

I know I shouldn’t base it off this since I haven’t been doing it for a month or more

I just need opinions and tips

To make sure I’m doing it correctly In the future …..