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.
Morgana is a champion that you need to be fast on i will told you why:
when u go for your lock u need to be fast to put your (W) out when they stand but be sure that the enemy is standing on it when he is locked.
Morganas ultimate is a AoE stun and damage that amazing, but when u decide to use it be sure that the enemy is in range for it hole time, if you not it will be interuppted on that champion that run away.
now to Morganas shield:
i always try to make the shield on the tank in the beggining of fight (or that champ that lose most hp and need to run away.
What the shield do is absorbing some magical damage and make the allied champion immune to stuns snare fear and locks .