Need help with beam

[DJ_Dogos]

Hello, i need help with a dust color beam (yellow) to make it from sky to it.
I have a half of skript, when it may on right click it shoots a beam from sky and damage entities around 5 radius around 4 thick block beam

 

[DJ_Dogos]

this is with i started

on right click:
    if name of player's tool contains "&fDragon Beam":
        if {dragonbeam.%player's uuid%} is not set:
            set {dragonbeam.%player's uuid%} to 300
            dragonbeam(player, 50, 20)
            play sound "minecraft:entity.blaze.shoot" with volume 3 at player
            send action bar "&cMusíš Počkat 15s, než využiješ &6Fire Ball &cZnovu!" to player
            wait 5 second
            send action bar "&cMusíš Počkat 10s, než využiješ &6Fire Ball &cZnovu!" to player
            wait 5 second
            send action bar "&cMusíš Počkat 5s, než využiješ &6Fire Ball &cZnovu!" to player
            wait 5 second
            send action bar "&aMůžeš použít &6Fire Ball &aZnovu!" to player
            clear {fireball.%player's uuid%}
            wait 1.5 second
            send action bar "" to player

but it has to be a function, but i dont know how it will be, i only know i have to start with

function dragonbeam(p: nearest entity, length: number, dmg: number):