I've never used these kits but here is the directions for the Low Range Nitrate kit:
"DIRECTIONS FOR USE
1) Following the "Guidelines for Accurate Tests Results", obtain a representative water sample for testing.
2) Open one reagent pillow marked LR NITRATE and add to the water sample, cap and mix for 1 1/2 minutes by inverting the test cube.
3) Open one reagent pillow marked LR NITRITE, add it to the water sample, cap and mix for 30 seconds.
4) Allow the mixture to react for 5 minutes and determine the nitrate concentration by matching the closest color on the comparator. After use, discard the contents of the cube and rinse with tap water. Do not return any rinse water to the aquarium or pond.
5) The reading given is for saltwater . For freshwater testing, multiply the comparator reading by 0.6 for the actual value.
6) Freshwater fish and invertebrates should be kept in the range of 35-70 mg/L nitrate or lower, and marine fish and invertebrates should be kept in water below 20 mg/L. Although tolerances to nitrates vary greatly among species, water changes should be performed when concentrations approach these levels."
This is just an example as I don't know which one you're talking about.
Which part of the above directions are confusing?
If it's their "color comparitor", it looks like the way it works is that it has two sections side by side. I think you fill the section that has the different colors on the back with aquarium water. The other section is the tested water sample...