There should be the little green circle at the center of your screen, unless you moved it. Left-click turns it red and locks it in place, clicking again makes it green and movable. Right click opens the main window.
On right click, it gives the main buff window, with a column for your aura, a column for each class, and then a column for pets. You click in the box below the class avatar to scroll through your known blessings, same with the aura button. Then when you click Refresh, close that window, and join a group with members of those classes, buttons show up next to the movable circle.
You then left-click on the blessing buttons or press the hotkey (default is comma, I believe) to cast greater blessings on each class you've set. Right-clicking (or it's other hotkey, I think period) gives out single-target blessings. On the class buttons, there's also a timer for the lowest remaining time on a blessing. If the timer is in the top half, it's a greater blessing. Bottom half is a lesser.
Above the class blessing buttons is your Aura notifier. Red means it's off. Blue means it's on. Grey means it's on but someone else is also using that same aura. If there's a name in that box, it means someone else with Pally Power has that aura set to them as well.
Below the aura button is the Righteous Fury button. You can set it to notify you when RF is off and then give a timer.
And below the RF button and above the class blessing buttons is the mass cast button. Left or right click on that repeatedly and it automatically casts the correct blessing type on the class or person with the lowest remaining time, or straight down the list if no one has buffs. It does not work in combat.
I think that's everything important..
Oh, also, in the main buff window, on the left side where it shows each paladin with Pally power, it shows the highest level of each blessing and aura for each pally, as well as how many points in the improvements to those blessings and auras. It also tells you how many Symbols of Kings and Divinity each pally has.