Well it sounds like it doesnt have limits, you would see them attached to each axis and they would get activated at at least one end of each axis travel.
So no limits then you need to do this if you want to use SoftLimits.
Go to your homing and limits page and put a check in the Auto Zero box.
Move machine to its extremes on each axis so that the tool is lower left and fully up. Mark some way on the tables so you can jog back to this position in future.
Then press the Ref All button
Next in Homing and limits set the X and Y min to zero and the Z Max to zero
Now Jog to the opposite extremes on each travel and look at the DROs and enter this value in X and Y max and Z min(X and Y should be positive numbers and Z should be a negative)
Now just enable the Soflimit button and you are set, you can set a larger slow zone on each axis if required.
One thing you have to remember is you need to move each axis to lower left and fully up each time you start Mach, this is why I said to mark that position. If you dont do this each time you start then Mach has no way of knowing where it is and so cant use the softlimits.
Hood