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.
This build is designed to take advantage of Morgana's built in combo. What's that? A combo, built right in for us? Why yes, it's described in the character's description. It's really quite simple use Dark Binding to stun the target and drop a Tormented Soil under the target while running up to them (preferably you will position your Tormented Soil so that the majority of the effect lies behind them and they must move through it if they want to run away) then when within range and while the target is still stunned use Soul Shackles. The target should attempt to flee at this point but being slowed (if you have your Rylai's Crystal Scepter they're triple slowed Tormented Soil and Soul Shackles both innately and from the scepter) they will have a hard time getting away and they will take more damage from the Tormented Soil since it takes them significantly longer to cross the intervening space.
Now, if the target is really fast, say Boots of Quickness + Phantom Dancer fast, this trick is doomed, I say doomed, to fail, so bring a friend with a second stun or some additional dps and take them down that way.
I've used this build quite a few times laning in the middle and the innate Morgana combo is good for at least a kill or two in the transition from early to mid game when you're a couple levels higher than everyone else. Use it on the middle opponent first until they get wise and hug their tower and then you scoot on over to the weaker set of opponents and make them suffer a bit.
Later in the game you can't take people down as easily by your self but your stun stays strong and your AoE damage abilities can be a surprise threat in group fights sometimes.
Oh, the shield, it's there, meh, save yourself or your teammates whatever, I'm not a fan of it but the build has enough AP that it's a life saver on occasion.
I think this is a pretty standard high damage Morgana build, the only real trick is the deathfire grasp which you should try and open with on the tank. The biggest benefit is that you can actually scare a high HP tank character out of the melee by knocking off 40% of their health in one shot, especially when they're used to being nigh invulnerable.