skript

[vagrant harbor]

command /hi
trigger:
send message "Hi" to player

what is wrong

[junior matrix]

hi let me explain you

https://docs.skriptlang.org/docs.html?search=#StructCommand that is the doc you need to read. to make a custom command, and, in your code the first line must end with a ":"

like "command /hi:"

and, in command, some effects do not need to place the player, since they react to the trigger, so message does not need "to player"

but in lines of events, yes, you need to use "to player"

and

you re missing one slash/tab

Take it like, when a line of code ends in : you need to use one more tab for the next line

[craggy plover]

could have just linked him a basic skript guide tbh