help! first time to try OPK

I'm 24 y/o and we've been trying to conceive for a year now. I only depende on apps or websites to determine my fertile days BUT it seems to not work. So i decided to give OPKs a try. My usual cycle length is 32 days. What day should I start testing? And if does become positive, does it mean that it's my fertile day or ovulation day itself? :)