Opk and pregnancy test 🙄

Kat
Hey ladies- 
Ok so I have been seeing so many ladies talk about they took their opk as a form of a hcg test🙄 I always asked how is this so ; but after I looked online it seems to be more common then I thought . My question for the ladies who done this is - when did you take the opk ? How many dpo??? 
Also if when you take a opk it always shows double lines how do you know if it's a good sign of pregnancy ? Are you looking for the line to b dark as when we test our surge? So many questions not enough answers lolÂ