Hi, I found them useful. You can buy expensive ones that display smiley faces etc but I had good success with cheap tests from Amazon or Ebay (cardboard little strips). I find these particuarly good as you get a LOT for your money, making you more inclined to test more frequently and therefore catch ovulation (short window to catch!)
Basically you wee on them when ovulation is 'kind of ' expected. Most packets advise you to start testing around day 10 of your cycle, with the expected ovulation time being around day 14 but everyone is different. The test strips helped me realize that I am NOT one of those people who ovulates on day 14. They are useful little things.
They have a 'control' line. (Usually a pink line) this displays when you wee on it. This just tells you the test is working. If you are ovulating, a second pink line will appear. (Technically I think it picks up a hormone just before ovulation) So If the line is about the same in darkness to the 'control' line, you are most likely ovulating shortly. Basically when you see a positive result, you need to consider DTD to catch the egg!
Sometimes, leading up to ovulation you DO display a pink line but it may be faint. This is not quite considered ovulation time/a positive result. Some people pick up faint lines easier than others. I always seemed to have 'all or nothing' either no line, or a good line, but some people go through fainter ones before the true positive.
The instructions are easy to follow and I do think they are worth trying..no where near as complicated as I anticipated either.