Hey chan, Really enjoyed your questions in the live chat!
You need three things to make laser light,
A power source: I use high voltage electricity
A thing to generate the light: The first lasers used rubies, I use a mixture of two chemical, Helium and Cadmium.
And a chamber to put them in, with mirrors at either end. This is called the optical cavity.
The electricty causes the (let’s say) ruby to generate a little packed of light, this little packet has enough energy to make copies of itself as it goes back and forth through the ruby, bouncing off the mirrors. The mirrors are designed to let a tiny bit of light through, so When you have enough light (Which all goes the same direction, because they’re all exact copies of that first bit of light) It can come through the mirror as a laser beam!