Need some help with arrow projectiles

[NitroN666]

Hey so I've just started messing around with modding, and I can't figure out how to change the projectiles of my repeater to shoot faster and with the same bone arrows as the marrow has (I basically want it the same as the marrow in terms of projectiles)

Rather than just sending an example would you please explain what the code itself actually means so that my understanding of modding expands!

Thanks!