Saddling over space time
The ring on the back will push, the ring on the front will pull
The Alcubierre drive is based on deformation of space time itself, creating a means of forward propulsion by folding (or warping) space time into a saddle surface around the ship, which looks like this (projected in 3d)
Note the ship is not sticked to the surface, as would be the case in classic models. The ship actually travels straight over space time, and the bent surface in front of the ship provides the shortcut over long distances. The amount of FTL depends on the amount of spacetime "bridged" by the ship's forward movement. The steeper the gradients are, the more space time will be shortcut and the faster your ship will travel.
Rings are different polarity
To create a space time valley in front of the ship, there needs to be a "positive mass", but that is not a real, physical mass, or any object mass. The ship's rings contain field generators that generate an artificial gravitational field, which causes the saddle surface in spacetime to exist. The ship "falls" into forward direction.
The saddle surface cannot have a single lobe. On the back of the ship, you have a similar generator that has opposite polarity: it will project a negative mass behind the ship, so the gradient (or perceived gravity) is negative.
The saddle surface is huge, it can span light years. But that mode of operation is only safe in interstellar space. In the first weeks of travel, the saddle surface will gradually expand, keeping the middle part tilted, in effect accelerating the ship. At some point it will travel FTL over the valley.. when arrived on the other side a new saddle is generated and the procedure is repeated, until the target is reached.
How you hit the breaks or change direction when using an Alcubierre drive
The ship is actually pushed moving over spacetime. That push ends when a platform is formed. The platform will look as follows:
While the ship is "on" the platform, it will experience 0G and travel with a single speed. It can decelerate, weaken the gradients, or change direction. During travel, the saddle's shape, allows some velocity control, but the ship can't change direction. The two wheels make the ship only travel straight forward, during FTL.
Mind the exhaust: gravitational wave interference
One little note I can leave about this ancient FTL warp technology: there will be side effects from using it. Your ship will affect the space it travels through. While it expands, the saddle surface will invoke gravitational waves, which are not healthy for life, when subjected to them at close range. For that reason, you can't switch an Alcubierre drive on, anywhere near inhabited planets. A distance of about 80 AU is advised, which is about 2x Pluto's orbit.