New to OPK

Help! Never used these & there are so many directions! Don't use 1st morning urine. Don't use urine held for long periods of time. Don't drink lots of fluids. Test twice a day but in the afternoon. Ahh! I'm a teacher so it's almost impossible for me to privately test opk at work. I, sadly, have to hold my urine for long periods of time & drink almost 1 gallon of water a day. Help...