Tension Meter such as PARK TM-1
Truing Stand. various brands.

Spokes tend to have specific tension "ranges", depending on gauge, use and various other factors. (and probably more arguments about what's best)
DS spokes on a rear wheel will have higher tension then the NDS spokes. (DS= Drive Side)

There's lots of tutorials if you use your search engine. Some very good and some not. Compare a couple different ones and you can kind of filter out the baloney.