Beginner Rapid Fire Help?

Today I am literally just starting with an Arduino and I have the uno model. I literally have barely any knowledge on how it works and know the basics. I do know a fair amount Java coding which and the Arduino code looks fairly simple.

Basically what I am trying to achieve is this: Arduino cookie clickers mouse hack - YouTube

The problem is I have no clue what parts I need, how to build it etc. The only thing I understand is how the code works which is fairly simple. I am also really confused on how this thing is somehow connected to the mouse???

Please use basic terminology if you are explain it as I really wanna build this.

Basically what I am planning on doing with this is to have a button that I can press to hold down to rapid click during a game that is producing clicks from a mouse. Then I plan on having another mouse which I can use to aim and stuff!

Thanks for your help!

For hacking a button get a relay module and connect its N.O. contacts in parallel to the mouse button.

DrDiettrich:
For hacking a button get a relay module and connect its N.O. contacts in parallel to the mouse button.

Gotcha. What type of relay module do I look for?

Any mechanical relay module, not SSR.