The website Shumie has suggested is a godo place to buy & I highly recommend them
OPKs can be used from around 8th/9th day of cycle counting day 1 as the first day of you period (if your cycle is 28 days+) - well thats my personal opinion. You need to test like you would a pregnancy test only not with FMU they say between 12-2 in the afternoon is best.
You have the control line that will always appear& the test line that will detect your LH serge & ovulation. A line as dark or darker than the control line is a positive and hopfully not only have you had a couple of practice Bds

but it would be a godo idea to get jiggy

the night of a positive result.
I would suggest buying the minimum of 10 tests!!
Good luck
