In Mari0 1.6, there were 3 faith plate elements, facing left, up and right. It was impossible to change the trajectory. In Mari0 SE, the 3 elements were reduced to 1, with the added ability to change the plate's trajectory. Despite there being wall and ceiling-mounted Faith Plates in Portal 2, they can only be floor-mounted in Mari0.
When the plate pops out of the ground, the space it previously occupied takes on the color of the level's background.(can be seen in the .gif) Change the color of your background accordingly for better visual effect.
When placed, they take up 2 tiles of space horizontally. To change a plate's trajectory, right click the faith plate entity and move the sliders. The plate's trajectory is shown via a blue beam coming off the plate. You can also toggle the plate on/off via input. When on, the light on the plate is blue and it can launch things. When off, the light is orange and has no effect on objects that are on top of it. This could be used to force a player to find a cube/button in the level to activate the plate, or connect it to a timer or squarewave.
In their most basic form, they can be used to fling things. However, they can also be used to create a bouncy floor, as seen to the right, or they can be placed directly underneath a portal surface, allowing the player to bring the plate and launch themselves anywhere.