Scoreboard basics

Three words to get straight first

Objective — One board, e.g. a kill counter. Nothing can be stored until you create one
Criterion — What the board counts, and whether the game updates it or you do
Display slot — Where the board is shown. Assign none and nobody sees anything

The number one confusion here is creating an objective and assuming that is it — you still need a second command to make it visible

Criterion	Who updates it	Used for
`dummy`	You, via commands	The most-used one, because you control everything — minigame points, for instance
`playerKillCount`	The game, automatically	Counting how many other players someone has killed
`deathCount`	The game, automatically	Counting deaths — the basis of a limited-lives system
`health`	The game, automatically	Showing player health next to their name
`trigger`	The player, via /trigger	Letting ordinary players make a choice without operator permission

When in doubt pick dummy — you stay in full control and it is easier to change your mind later

These three steps always run in this order. Skip one and it looks like nothing is working

/scoreboard objectives add kills dummy "จำนวนการฆ่า"
/scoreboard objectives setdisplay sidebar kills
/scoreboard players add @p kills 1

The first two lines are one-off setup. The third is the one that goes into a command block to run over and over

Slot	Where it shows	Good for
`sidebar`	The panel on the right of the screen	The main scoreboard of a game — the most visible option
`list`	The player list when you hold Tab	A number people should see only when they go looking
`belowName`	Under the nametag above a player’s head	A value others should read from a distance — health, or lives left

A slot shows one board at a time — assigning a new board to the same slot immediately removes the old one from it

A score becomes genuinely useful once you filter on it, which you do inside a target selector’s square brackets

@a[scores={kills=5..}] — players with a score of 5 or more
@a[scores={kills=0}] — players still on zero
@a[scores={lives=..0}] — players who have run out of lives — switch them to spectator

Combine it with execute and the whole system runs itself — announce a winner the moment anyone reaches 10 Read about execute

Symptom	Cause
Created a board but nothing appears	You have not run setdisplay yet
The board shows but everyone stays on 0	You used dummy, which the game never updates — you have to add points yourself
A long board name turns the command red	Names containing spaces must be wrapped in quotes
Scores carry over into the next round	You must run players reset or set them to 0 — nothing clears itself at the end of a round