Temperature test?...

Nikki • My husband and I have a soap opera/lifetime movie story behind us. Long story short; best friends since `08, married `15
I stopped my birth control in July and my husband and I have been TTC since. I know there can sometimes be a delay if you were taking birth control, however I was only taking my BC for 2/3 months. Still nothing. Glow is telling me to "take my temperature" starting tomorrow. I've never "tried" to conceive so I'm curious as to what taking my temperature consists of... Is this oral temp? What's the purpose behind it?