How does slicer work, how fast is it?

I am thinking about messing around with slicing .obj/.stl file into gcode or maybe even remove the gcode step and move straight to motor direct control.

I am only thinking about this as I heard slicing is very slow, I have never used any slicer, what is slow about it, how long does a slicer take to turn a typical object into gcode?

Is there an easy to understand overview of the slicing process and how the slicer code works?

Slic3r is very quick. Seconds to slice into gcode.
It's fee download and try it out.

Slic3r is about as fast as you can get. Time depends on the complexity of the object. It can take anywhere from a few seconds to several minutes.