To the experienced builders. What are the absolutely neccessary tools to build a reliable trued wheel? The wheel will be a 700c wheel for a standard road bike.
There are definitely more sophisticated tools for this but in my mind the essential kit includes (1) the right-sized spoke wrench, (2) a flathead screwdriver, (3) grease for spoke threads, (4) the front dropouts on an upside-down bicycle with brake pads for truing, and (5) lots of patience if you haven't done it before.
All of this assumes you have a rim and hub with the same hole count, along with correctly-sized spokes and enough spoke nipples.
To properly true and tension a wheel:
You can, of course, jury rig a Truing stand as others have mentioned, and you can build without a way to measure the tension on the spokes. Without a lot of practice and skill, though, your wheels will be less than perfectly strong and straight.
You should use a thread locker on the spoke nipples. Ideally, Spoke Prep from DT Swiss, or Linseed Oil, which acts as a lubricant until it dries, but acts as a thread lock once it's dry.
The book at the end of the list will teach you the theory behind how a wheel is built and why, and the lacing patterns, and what works best, and why.