so, good news is Zita says you can keep that thermometer in your gob!
temp has to be taken on waking (after at least 3 hours undisturbed sleep in theory but that hasn't caused me too much issue).
you have to take temp before you do anything else, so no getting out of bed. this is why mine lived on my alarm clock on top of the snooze button so I would remember to do it when I was woken by the alarm.
your temp is lower in follicular phase (time pre ov) and rises about 24 hours after ovulation.
ovulation is confirmed when you have 3 days of high temps.
high = above "cover line" kind of like the mean on a graph in maths GCSE. the apps do it for you.
ovulation dips are a thing but completely unreliable so don't waste your time looking for one.
same with implantation dips. they are a thing but if you get a dip a 7dpo it could mean you are pg or it could mean fuck all so don't do it to yourself. take it from someone who knows!
a day or so before AF the temp will drop. sometimes mine hasn't dropped until cd1 or cd2 so again no drop means fuck all.
this is why I don't temp after ov confirmed.
all the above happens because progesterone (released by the corpus leuteum (follicle egg came from) after ovulation) in your blood makes your body temperature increase.
similarly the drop in progesterone causing af signals oestrogen to come back into play which is why you sometimes get ewcm just before AF.
oestrogen is the pre ov hormone which opens the cervix and creates fertile fluid.
any questions class? 
I'll try and post a link to my chart for you