How to walk while using Azmodan's All Shall Burn ability? I see people do it. But when I channel and start to walk the ability stops, if I walk and then channel I stop.
On level 13, you take the talent March of Sin that makes you able to move while using your ability.
Azmodan can move at 75% speed while channeling All Shall Burn.
Note that you can try any hero, even if you don't own it, from the Shop tab and pressing "Try" button. You can try every hero (every skin) and see how they work, as well as experimenting with their talents.
As of the 1/4/2017 patch Azmodan can walk while channeling All Shall Burn at 40% move speed by default without talents. Additonally, the level 7 March of Sin talent increases the move speed while channeling to 80%.