Help with gerber file format please

[boylesg]

Question for anyone familiar with PCB design and Gerber file format.
I have been reading this document but unfortunately it contains too much engineering gibberish and not enough simple explanation

X-2794000Y-254000D2*
D14*
Y-508000D1*
X-2286000Y-762000D2*
X-2540000D1*
X-2794000D1*

It seems obvious the the X and Y denote the x and/or y coordinates of a point in a polyline.
And the D1 and D2 denote move to and llne to commands

But hat are the units here? Are those integers referring to steps (as in a stepper motor) or millimeters or something else?
But I can't figure out what all of this means.

%TF.GenerationSoftware,Novarm,DipTrace,3.2.0.1*%  // This is just the software that generated the gerber file
%TF.CreationDate,2018-11-07T12:25:27+09:00*%     // And the file date....all good
%FSLAX35Y35*%                                                           // What is this?
%MOMM*%                                                                    // What is this? 
%TF.FileFunction,Copper,L2,Bot*%                                // Copper clad board but what do L2 and Bot mean?
%TF.Part,Single*%                                                         // Single sided PCB....all good
%TA.AperFunction,Conductor*%                                    //
%ADD14C,2.0*%                                                            // What do these two lines mean?
%TA.AperFunction,ComponentPad*%                            // Get this....all good
%ADD15C,2.3*%                                                            // My pads in diptrace were circles of 2.3mm diameter.....all good

[ataradov]

Gerber files are described by the standard RS-274X. Here is the document: http://www.apcircuits.com/Portals/0/Assets/Downloads/the_gerber_file_format_specification.pdf?ver=2015-06-13-175030-363

"%MOMM*%" - this sets the units to millimeters. "%MOIN*%" would be inches.

[SiliconWizard]

%FSLAX35Y35*%                                                           // What is this?
%MOMM*%                                                                    // What is this? 

Those are the two function codes that define how coordinates are to be interpreted in a Gerber file.

MOMM => coordinates are in mm
FSLAX35Y35 =>  omit leading zeroes, absolute, X and Y coordinates in 3.5 format (meaning 3 integer digits and 5 decimal digits)

Strongly suggest you read the spec. doc as ataradov pointed you to.
I'll give you the official Ucamco page though: https://www.ucamco.com/en/file-formats/gerber/downloads