/setblock

Places a block at a specified position in the world. Can optionally destroy the existing block, keep it, or replace it.

Syntax

/setblock <pos> <block> [destroy|keep|replace]

Name	Type	Required	Description
pos	block_pos	Required	The coordinates where the block should be placed.
block	block_state	Required	The block to place, optionally with block states (e.g., oak_stairs[facing=east]).
mode	literal	Optional	destroy = drops old block as item; keep = only places if target is air; replace = overwrites (default).

/setblock ~ ~-1 ~ minecraft:diamond_block

Places a diamond block directly below you.

/setblock 0 64 0 minecraft:oak_stairs[facing=south,half=top] destroy

Places a top-half south-facing oak stair at 0,64,0, destroying whatever was there.

/setblock ~ ~ ~ air

Removes the block at your position by replacing it with air.

Using 'keep' mode and not realizing it silently fails if the position already has a non-air block.
Forgetting block state syntax uses square brackets and key=value pairs separated by commas.

Block states are specified in square brackets, e.g., chest[facing=north]. Use /setblock with air to effectively delete a block.

Try these commands on Astroworld or host your own server.