How to create a constellation on mouse click?

Hi! I'm fairly familiar with Unity, and have made a few games. This game is a constellation-creating game. I need to write a script that will allow the player to click a star, and have it connect to another star. I think I will need the line objects to instantiate on click? I'm testing out with a box object, which is enabled as a trigger, and I'm not too familiar with instantiating objects or making them visible, so all I have is a void OnTriggerEnter() ... LOL.

Sorry if my typing is jumbled, any help is appreciated!