BBT and ovulation question

Jo • I am a nurse, wife, and mother to one sweet baby girl age 7, and one sweet baby boy age 2, who gained his angel wings on May 18, 2015. We have been trying for #3 since 9/2014. With no luck.
I'm new to temping. I'm going through an early miscarriage right now, but as soon as I stop bleeding, we're trying again. So here's the question, I also use opks, but exactly how do you tell you've ovulated by your temp? Does it go up or down? And what about after ovulation? Can someone explain the temping process to me and what I need to look for in my temping chart to make sure I'm actually ovulating. II yest had the Mirena surgically removed September 2014, bc it had migrated and embedded in my uterine lining, I'm hoping this didn't mess with my ability to conceive and carry the child. We've been trying for 10 months now, and finally conceive, but miscarry early. I'm just confused about the whole chart thing. Please help.