Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
"Nice one Ashe, way to support the team."
I've got these type of comments a few times. This is also true, Ashe is a great support/damage character to use.
Ghost: This is a very useful spell for Ashe because she is really squishy in the beginning and is pretty slow overall. With ghost, you can get into team fights easier, escape when possible, or just be plain annoying.
Heal: When your HP is low, heal can keep you alive for a bit longer, it can also heal your whole team(if they are close enough) when they are in team fights, you can heal everybody and keep them alive while the other team rages that they all died without getting a kill.
This build overall is pretty good for a DPS, An AP build for Ashe is useless except for her Ult, other than that, your just food for the other team.