Hi Darryl,
If you connect 5 volts across the input side of your SSR (observe correct polarity) with a series ammeter you can measure the drive current. If it is less than 10mA then your SSR can be driven directly from your breakout board.
Choose the output pin you wish to use then connect the SSR input between this pin and GND, configure Mach3 Ports & Pins / Output Signals / Output #1 to your chosen Port and Pin then set it Active High. Then Under Ports & Pins / Spindle Setup choose Output #1 for Clockwise(M3) you can also set the spin-up and spin-down delays (If required).
Adding M3 to you GCode will then activate the SSR and the code M5 will de-activate it.
Tweakie.
nb. I could do with a bit of your warm weather here in the UK, it's Brass Monkey's in my workshop.