I don't know either, but 30 seconds with Google suggests it's a soil test kit for NPK. Some say these kits are not very accurate, most here agree a lab test is better and not that expensive. If the test says you're low in one more more nutrients, presumably you'd add those in the form of compost or fertilizer. One thing about a lab test, most ag labs will make recommendations on amendments in lb/1000 sq ft. I don't know that you'll get that with a home test kit.

LaMotte makes and sells a variety of test kits for soils and pools that rely on diluting a sample with a reagent. The pH test will tell you whether the soil has a low pH or a high pH but not why or whether the Calcium to Magnesium ratio is near to balance, so you might add Calcitic lime when you nee Dolomitic and not make much progress correcting that soil. These tests for the other nutrients present the same problems, a low test result may mean adding a quantity of some nutrient but not how much.
State Ag schools, through the Cooperative Extension Service, provide soil testing services and also provide recommendations about correcting any nutrient deficiencies found. If you live in a state where this service is not provided your Cooperative Extension Service can help find a soil test lab and either UCONN or UMASS will do testing for others outside of those states.
Considering that most of us only need to test the soil about every 5 years a soil test kit may not be a very good investment.