Hi Jennie
The sticks you refer to are called ketostix and they are about 4 quid for a packet of 50 , basically you pee on them and if you are in ketosis they turn a shade of purple, if its really dark purple you need to drink more water the lighter the stick the better as it means you are not dehydrated.(it goes from pale pink to kinda barbie pink to purple you want pale pink(ish) But sometimes it shows a negative reading if you test at the end of the day as drinking all the water we need to drink flushes the ketones out of your system so the best time to test is in the morning
Hope this helps