Not clear whether you use Mac or PC. On a Mac, the program Barfly allows you to compose in ABC on a split screen, so you see instantaneous results.
That said, its best to open an existing tune and study it. Basically, you have a series of defining fields (ID no, Title, Key, Time Sig, etc.) that need to be in a certain order. Then the tune begins, with the note names, either in lower or upper case, divided by bar lines. You modify things from there, including accidentals, slurs, ornaments and guitar chords.
Its ingeniously easy but best for diatonic music, like Irtrad. If you try and get too fancy (i.e. chromatic or multiple voice), you might as well go into a true notation program.
I use abc a lot, mostly to put together tune sets and distribute via pdf to the band. I am committed to original tune sets, so its not a matter of telling somebody to listen to an Altan record or something to learn a set of tunes.
Because its freeware, it doesnt have the smoothness and functionality of a major piece of software. There are idiosyncracies and variances between the various available programs. Also, rendering it in clean form, which involves postscript conversion, has some peculiarities.
Another problem with it being freeware is that the descriptive language on the ReadMe files isn’t carefully designed to communicate with everybody, which a lot of proprietary software attempts to do. So you might feel like you are on the outside of a dirty window trying to look in, while others “get it” immediately. I am notoriously bad at reading instruction manuals etc so I ignored a lot of the readmes until I got in a pickle. Still, I mostly just find a jig that I know, and study the fields etc to get it right. I always forget certain things (like how to notate a roll) and have to open up a reel with a roll and copy/paste.
IF I have correctly rendered a tune, I can drag it onto ABCforMac and it generates a great postscript file. I distill that with Acrobat Distiller then get a very nice pdf. But sometimes, if only one thing is wrong, I won’t get a finished .ps. In that case, I use a very rude and crude YAPS which does the same thing but comes out sloppier.
Happy to answer any other questions here or PM, but I am on Mac so it might be inapplicable to your situation.