Help, no clue what I’m doing!!!

Alicia • Mom to a 14 yo boy and 8 yo girl. One 👼🏻 11/2010.

So with my 2 kids I didn’t do any OPK or temping. Now for the 3rd I am, mainly bc I’m not in my 20s anymore. I get the OPKs BUT I get the temp deal. AF will be gone tonight or tomorrow. I’m going to get a thermometer in the morning bc I don’t have a basal one. Can someone explain temping to me???