what's an Easy Way to Detect Clicking within a Script?

I know the question has been asked several times, but, in a 2D plane, what’s an easy way to detect clicking?

I have a 2D platformer game where you click on NPCs to interact with them. Step by step, what do I have to do, in the scripting and using components, to have something happen when I click.

Yes I know that was very vague but this is a more or less complicated question.

Just add “2d” to your google search.

Use the OnMouseDown method.