Signals and connect as a beginner

Godot Version

4.2.2 mono


I am very much a beginner and I have just finished middle I would like to know how to send signals to nodes in a dynamic scene.
What I mean by that is I want to send a signal every time a bullet that is a separate scene before being created hits something this signal would than call a function in a separate script remove 1 from a variable enemies_left. I am having trouble with the signal part, the collision detection and bullet creation are not a problem.
The enemy is from the initial scene where the player is and later the bullets spawn in. Thank you.