Ovulation Test. How do they work

Angie
Hello everyone, 
We are TTC #3 baby, our last baby. And after being on IUD for about 3 yrs my cycle has been all over the place 29-33 days. I try for the first time the ovulation test but I don't know how it really works. I got one faint line and one bright line. So am I ovulating? My 2 pregnancy were always on time 28 days so when app said fertile we got pregnant. I started this app to see if it works. 
AF is Oct 22. Any ladies with same AF? 
Let's hope it doesn't come