Cm check and bbt

Lauren
Hey ladies,
This is my first time ttc. My lg wasn't planned. I came off the iud 14th Nov and had af 4 days ago. Stopped yesterday.
How do I do my bbt? And when I do a cm check what am I looking for? also what do they mean by cervix low/mid/high?
Sorry for all the questions.. So confused 
Thanks in advance