You can also chart your temperature, your bbt increases the day after ovulation, however if you wait for the temperature rise it's then too late in your cycle to conceive. Over time though it can give you a better understanding of your cycles. Opk tests will detect the LH surge which gives you an indication ovulation is likely to occur soon. Fertility friend is a very useful site for information and it's free to join and use the temperature charting system .
U know ur ovulating by getting ewcm (egg white cervical mucus) or ovulation pains, or getting a positive on a ovulation test, that's best way to know for sure. On average most women ov about 14 days before their period starts. Hth xx