Do I have the right test?

Ive been doing alot of reading and browsing and Im wondering if I have the right test kit. In regards to alkalinity, I have a KH test kit. But in reading theres mention of KH, GH, ALK. Some test kits Ive looked at list one or the other, or 2 of the 3 but not all 3. My kit goes over KH and GH but only has reagents for KH. A few articles I read say all 3 are related but are they the "same", or should I be testing for all 3. No current issues, tank is a little new, starting to see a decrease in some parameters and have been reading more about them all.