The trick here would be to make a blueprint for your fireball. One of the properties you can add to a blueprint is “projectile movement”. (found in the components section, under “add component”). Then, if you spawn that blueprint facing in the correct direction it will whizz away at whatever speed you picked for it.
Here is a walkthrough tutorial by tesladev that explains the entire process! His channel contains a lot of useful videos on this. There are also the unreal tutorials by zak parrish which are very thorough and will take you through the basics of blueprints etc.
Good luck!