Beacon turns a nether star into a standing area effect, which makes it the one block whose real cost is a boss fight. It sits on a pyramid of mineral blocks — iron, gold, emerald, diamond and netherite all count and can be mixed in the same structure, so iron from a farm is the practical way to build one.
To activate it you need the beacon pyramid beneath it, a single iron, gold or netherite ingot, diamond or emerald placed in its slot, and a clear line to the sky. Each extra tier widens the range and unlocks more effects: Speed and Haste at the smallest, then Resistance and Jump Boost, then Strength, and a four-tier pyramid opens a second slot for Regeneration or for raising the primary effect to level II.
When a beacon is not working, the beam is almost always why. Any solid block above it stops the beam and the effects with it, while glass, stained glass, water and other transparent blocks let it through. Stained glass also tints the beam, and stacking different colours blends them, which is how coloured beacon columns are made.
Range runs from roughly 20 blocks at the smallest pyramid out to 50 at full size, measured from the beacon itself, and the effect refreshes for as long as you stay inside — step out and it fades after a few seconds. That is why so many end up set to Haste and parked at a mining site or a build: within its radius it pays the star back every time you clear a chamber by hand.