Just dip a strip into the water and remove immediately. Do not shake excess water from the strip, just hold horizontally for 15 seconds and compare the colours on the strip pads with the colour chart on the side of the bottle.
When sanitising your hot tub with chlorine you should test the water at least twice weekly and adjust the total alkalinity, the pH and the chlorine level. . When sanitising with bromine test at least weekly. This is important because the sanitiser will only work effectively over a small pH range and that pH range must be maintained to keep your hot tub safe to use.
Store in a cool dry place and do not let the strips get damp.
NB. The accuracy of the readings will deteriorate after the use-by date printed on the pot.