Short Introduction:
1. Choose a hero by double-clicking him.
2. Choose three normal abilities and one ultimate.
3. Now you will fight creeps in your lane, 15 creeps spawn with a three second interval. 10 rounds for every race (Human/Orc/Night Elves/Naga/Undead).
4. Every fifth level is the time for the arena. Here, different modes can be set to alter the gameplay.
For the main site for Custom Hero Arena Defense, full changelog and more info go here: http://www.thehelper.net/forums/showthread.php?t=121339