how to make a hammer that with the right click does damage in a 6x6 area

This is tricky, you can create a custom block that has no texture and you can walk through, make so that on block collision it will damage the entity and destroy itself, also create a timer inside on block tick so it will destroy itself in a couple of ticks. Then on right click of your hammer it will spawn 6x6 blocks of those, it may damage the player but you can set up as IF entity not is subtype of player DO damage inside on block collision procedure, remember to mark "enable tile entity and inventory on this block"

it's actually super simple,

just make a function that runs the command,

execute at @e[distance=6,type=!player] run effect give @s minecraft:instant_damage 1 1 true

then make a procedure for on item right click that runs the function

:)

@e[distance=6,type=!player] run effect give @s minecraft:instant_damage 1 1 true

Why are you using commands... This is already possible in MCreator I believe, if not, super easy in custom code.

You can use;

World::getEntitiesWithinAABB

This give you an iterable list, now to damage entities just do something similar to;

Entity::attackEntityFrom

execute at @e[distance=..6,type=!player] run effect give @e[distance=..6,type=!player] minecraft:instant_damage 1 1 true 

write this instead

Oh and for the particle