Unfortunately Mach 3 is far more complex than being able to knock a few things together over the weekend, and be ready by Monday.
There are many things to learn, and before designing your own screens, then learning the workings of the ones on offer must come first.
I assume you have set up your system, from what you say, and you have the axis working. I can only suggest that you use the standard 1024 screen(s) set to start with. I, personally, would not even try to write a full screen (s), even though I know my way round the system fairly well. The 1024 set has been designed by the man who designed Mach 3 and must, by definition, be a good start.
It seems to provide all that is required to do some useful work. It has a choice of screen (not for everyday use) to set up the machine, to do diagnostics, to set up offsets - as well as the three main screens.
Screen 1 is the general "maid of all work" and you can control the entire machine from this. If you are doing a small job, and typing in instructions on the MDI line, then you use page 2. This also contains enough information to know what the machine is doing. Page 3 supplies a much simpler screen set with a large tool display. You can still control the machine from here, but it intended for you to switch to this screen for the tool display, and switch back.
You can switch between screens whilst the machine is working. You can make minor alterations to the screens quite easily, which is the best way to start - if you need to alter things. For example, jogging is not available on all screens - you could soon add it.
Most DRO's can be altered. There are some that read information from Mach3 only, but the positional DRO's, the Tool DRO, the Speed DRO can all be written to. Click on the DRO (it will light up) - type in the new information - PRESS RETURN. If you do not press return, the display will revert to the previous information.
The axis positional DRO's display 2 positions - one is the machine co-ordinates, the other work co-ordinates. Machine co-ordinates relate to the homing switches fitted (or not) on your machine. Professional machines have homing switches fitted, and the first job of the day is to home the machine. This puts the table (or cutter) at a position the machine knows, and resets the DRO's to zero. Mach 3 has the equivelant switch "Ref All Home". If you have home switches fitted, then the machine will home. If you do not have home switches set up in your Ports and Pins table, then the DRO's will merely zero without the table moving. You cannot change the machine co-ordinates other than by zeroing them using this switch. Once it has homed, the machine now knows where all other "things" are (e.g. automatic tool changer - chuck centres etc). If your homing switches are not operational then all you have done is tell the machine to regard this poisition as it's new home.
When the machine is moved to a position ready for work, the machine DRO's will change until it gets to a point where it is to start running your program. Dependent on how you (or your CAD) have written it, the position at which you start may vary BUT if you now press the Machine Co-ordinates button, the DRO's will now display the work co-ordinates (or program co-ordinates) - THE FIGURES WILL BE THE SAME HOWEVER. We will pretend you have jogged your table(or cutter) to a position that your program knows as 0,0 (usually the bottom left hand corner of the table). You can now ZERO the work co-ordinate dro's either by using the zero buttons, or typing zero in. If you have jogged to another position to start , say 10,15 then you can type that into the DRO's instead.
If you now press the Machine Co-ords button (i.e. the button surround is lit) the display will still show you the original machine co-ordinates. Toggle it again (the surround goes out) the display will show you the program co-ordinates that you have just set.
The program co-ordinates also record changes to the tool offsets (and any other offsets that you use). Tool offsets are entered in the Tool Table - see Config/Tool table. Enter in the information in the table - the name - e.g. 9mm drill and the diameter (which MUST be in the units you set your machine up in - e.g. 9 mm drill - 0.3543 inches diameter. Dont forget to press return and apply. The details will be saved and available next time you use the machine. There is no tool 0, which means that if you use tool zero all its measurements are 0 as far as offsets are concerned. Length and wear are not important (unless you have an automatic tool changer)
The ideal program would be - set all home - select the machine offset to move to the workpiece - use imperial (or metric) - select the tool(s) in order with diameters and lengths - cut the work - move the cutter out of the way so you can admire the finished product.
It doesn't actually take all that much doing - setting the machine up takes about 5 or 6 GCodes in a program, once you have it all "set up" on the ground.
I suggest you look through the Tutorial videos which cover a lot of the basics. I downlaoded them onto my machine, and I can refer to them when I want to.
If I've covered a lot you already know, I apologise - once I get on my soap box!!