Conveyor Belt (Clockwise)

Two versions exist, one running each way, and they are really the same block. You can convert between them at a crafting menu, and running wire to one flips its direction on the fly, so there is no reason to hoard both. Conveyor Slimes drop the clockwise one. Once you are in Hardmode the Steampunker stocks them, which is the sane way to buy the quantity any real build needs.

Belts move a specific list of things and not everything. Players, dropped items, town NPCs, critters, slimes and placed golf balls all ride along. So do a handful of enemies that normally sit still, including gnomes, ordinary mimics, lost girls and bound NPCs. Regular hostile enemies do not move at all, which is the single biggest limitation and the reason people still learn hoiks for enemy transport despite the fiddly setups. Falling blocks like sand and slush convert into items the moment they land on a belt, which is convenient for collection and annoying if you expected a sand column to stay a column.

A belt runs from the moment it is placed; nothing has to power it, and wire is only ever for reversing direction. A hammer gives you half blocks and slopes, so a line can climb diagonally, and belts will carry items straight up as well. They keep working through water and through lava, as long as whatever is riding survives the lava. Under a Gravitation Potion or a Gravity Globe the underside stops pushing you, which quietly breaks any upside down walkway you built.

The classic project is a Fallen Star collector: a skybridge of belts spanning the world and feeding one point at the center. It works, but belts are slow, and on a large world a good share of the night's stars never reach the end before dawn. The other thing worth knowing for farm builders is that an enemy spawning on a belt takes its type from the single block directly underneath the belt, rather than from a long search down the column the way platforms and planter boxes do. That makes belts a precise tool for controlling what appears, provided you remember which block is doing the deciding.