Channel is a spell made by Blizzard that was strictly used for triggered abilities (Custom abilities and spells that use triggers to get their effect). Therefore, Channel doesn't do anything when cast, but has more customization options.
The Base Order ID is the ID of the spell. In Channel, if we change it, it actually HAS an effect. Changing the ID can help because if a hero has two abilities based off the same ability, their IDs get messed up and he'll try to cast both. Changing this in Channel will change it's ID to something different, meaning you can have multiple Channels on the same hero.
Target Type is the type of target you select. If you want it to be instant meaning no target, if you target a unit, ground, or both.