Briefly:
> is to indicated a dotted note followed by a half note eg c> d would indicate c for 3 half-units followed by d for 1 half unit

The notes within parentheses are joined by a slur

H is just a fermata over the following note

z is a rest.

There is an introductory thread on abc: Midcat ABC Tune Guide

You can find an introduction to abc at Chris Walshaw's abc Home Page (the originator of abc). You'll also find links there to software to convert the abc to a midi file or to a postscript score.

Alternatively, you might look at The abcPlus Project

Mick