I take it you have downloaded Mach3. If not, do so. I assume all your cards are connected and wiring completed.
If not, don't worry, becasue you can learn a lot on the workbench, before bothering with the machine. The advice to look through the videos is good, I found them very informative, and if you download them, you can refer to them whilst working on the mill.
If you want to know where to start, then getting the axis moving would be the first thing. I might bore you ( and I have a feeling the Probo boards might already have a lot of this pre organised - however -
Mach 3 needs configuring to run your set up. This is where you need to start thinking. The first thing to do is configure the axis drive motors. These (as far as you are concerned) run on two wires, a "step" wire and a "direction" wire. These two wires go from your breakout board to a driver board (if you have a one piece board they might be already connected internally). There are two wires for each axis. There are normally (but not necessarily) from pins 2,3 - 4,5 - 6,7 and 8,9 on your breakout board to axis x,y,z and a.
To configure these you must start on Config/Motor tuning. Each axis has a page and what you must do is work out how many "steps" (or better word is pulses) the computer has to put out to move your axis one unit (decide NOW if your are working in inches or millimeters). It doesn't stop you running GCode in either measurement, but you have to set your machine up in all the same units.
Example - my motors are 200 steps per rev, and running at 1/8 step - i.e. 1600 per rev. The are geared down 3 to 1 to the leadscrew - 4,800 per turn and the leadscrew needs 10 turns per inch - 48,000 per inch. Enter this in the configuration . Calculate the other axis and enter them. Do not bother with velocity yet - enter perhaps 5 (easy to increase) and acceleration as 1.
In Port and Pins first page make sure port 1 is enabled - ignore the rest. In Ports and Pins/Motor Outputs fill in the information for each axis - as you have wired it - and then enable the axis - make sure ALL the information is in the line. If you are only trying say, one axis, then only fill in that line and enable it. Try jogging the axis - be patient - the jog control takes a bit of getting used to
That is enough diatribe from me - it should at least give you a start - and make a bit of sense of the videos and other information that is available.If you get the axis moving you can increase the speed until the motors start stalling and loosing steps - but bear in mind you have no safeties fitted yet and you do not want expensive collisions at the end of a run. You can jog the axis up and down, or better still start in the middle of the table (set all the DRO's to 0) and try a few GCode commands each way to move the axis - you can enter these manually - e.g. G0 X1 will move the table 1 inch G0 X0 will move it back G0 X1 Y1 with move it diagonally.
Try with callipers or whatever to see if your axis does move 1 inch as you have told it to. Bear in mind backlash - but that is another story.
Any more problems come back