Help pls ty ".
There are two events that can do this;
Fired when the left mouse button is pressed down
Fired when the left mouse button is fully clicked(pressed and released)
This is the script you're looking for:
function onClicked(mouse) print ("Hello World") -- Replace this to what you want your script to do end script.Parent.MouseButton1Click:connect(onClicked)
As Goulstem said, on the last line, you can replace the "MouseButton1Click" to "MouseButton1Down" if you want.