I wouldn’t be able to make a laser myself, but I know roughly how it works. In some sense it is a bit like a playground swing, if which you move your body back and forth at the right rate to pump more and more energy into the motion of the swing. This is knows as a resonance.
In a laser, you have a cavity with mirrors at both ends usually filled with some gas. When you put a electrical current through the gas, it excited some of the gas atoms to a higher energy state. After a while they return to the ground state and emit some light. This light bounces back and forth in the cavity, so it forms a standing wave.
Now, it turns out that when you continue to excite the gas atoms with the electric current, they start to resonate with the light wave, pumping more and more energy to it, just like you do in the swing. This leads to a very intense, coherent light. If one of the mirrors lets some light through, you get a beam of this light coming through it, and that is a laser.