Hello.
In the first picture in the link you shared, Get All Actors of Class is used to basically get all the Actors in the scene which are of the class type specified in the dropdown. Since there may be many Actors of that specified class, there will, of course, be many Actors to return from the Get All Actors of Class node. The way this node returns them is in an Array (That’s why the return node looks like a square made of smaller squares - that’s a symbol indicating that this node returns an Array). Normally the return node looks like a blue circle, like the As Projectile Base return node on Cast To ProjectileBase you’ve got there.
So since Get All Actors of Class returns an array, the GET node will retrieve a particular element from that array. Notice the get node has a number box with 0 in it. This is the index of the array. Arrays start at 0 so this is saying GET the first (0th) element in the array and return it.
So basically in that example, the way the Actor is accessed is through Get All Actors of Class (not a very efficient way, since it does what it says, gets ALL actors of the specified class which could be many) and then after that, it casts it to whatever…
Also rather than finding GET in search, just drag off of the square looking node on Get All Actors of Class and type GET. That should work.
Also I’m noticing you already are getting actors of the class ProjectileBase, so I wouldn’t think you’d need to cast it to ProjectileBase. It’s already the type you want. So you can just use GET, indexed at 0 (and this will retrieve the correct one if you’ve only got a single ProjectileBase instance in the world) and then simply call the function from that blue return node from the GET node. The blue return node is the ProjectileBase object retrieved from the Array returned by Get All Actors of Class.
Hope this informed you on the mechanics of those nodes you’re using.