There are of course many different combinations of breakout boards and specific controller add ons. Mach 3 can interact with various flavors of board to give spindle control, weather it be on/off through as a toggled switch, or step/dir pulses as if you were controlling a servo or stepper.
The number of inputs and outputs on a PC parallel port is limited. By the time you've put in step and dir for each axis, and a couple of other functions, you may quickly run out of IO. In order to get more IO you can add a second parallel port to the computer, and if you need to, hang another BOB off of that.
Mach has a bunch of good videos on their site that explain a lot of this setup and configuration of the software, they are well worth checking out. Get the basics running first, then move to stuff like spindle control and jog pendants.