One of the challenges that you will face initially as a new crusader is effective wrath management. Some of our main abilities (Fist of the Heavens for example) can be very costly. As a direct result of this, many crusaders, particularly while leveling, will start off with builds using Blessed Hammer [Burning Wrath or Thunderstruck] or Sweep Attack [Blazing Sweep], as they are much less expensive.
You will also want to use either Heavenly Strength or Fervor for one of your passive slots, depending on whether you are using a 2-hand or 1-hand weapon.
For a primary attack (wrath generator), if you like a more "in your face" melee style, I'd recommend Punish [Roar]. This gives you a nice defensive boost, and if you have decent block chance on your shield (without additional block chance, they range from 10% to 20% block chance) it can add quite a bit of damage without actually spending more time attacking. If you prefer to keep your distance, Justice [Crack] is a solid choice.
You'll also find that while leveling, Laws of Justice [Immovable Object] is a tremendous defensive boost since you cannot find all resistance as a stat on gear until a bit later.
Also, an important thing some newer players overlook...if you haven't already, turn on "elective mode" in the options menu. By default, the game limits your skill choices to 1 from every category...this need not be the case. Elective mode allows you to choose any skill combination you want.
To give a very very basic build idea, I would recommend something like this for leveling:http://us.battle.net/d3/en/calculator/crusader#aeTdiV!ZYUi!aaZbZZ
I've tried to tailor this to use runes unlocked around your level. Remember, Fervor passive and Heavenly Strength are interchangeable depending on whether you have a better 1-hand or 2-hand weapon. Also, it's probably wise to steer away from long cooldowns like Akarat's Champion as they are not as effective until you have significant amounts of cooldown reduction on gear.
Using Provoke with a large group of monsters in range will restore a huge amount of wrath, and will also keep the monsters in place for Condemn. So a general pack of monsters would go something like this:
1) Approach monsters and hit once with Punish [Roar] to activate the buff that damages monsters whenever you block.
2) Provoke to keep the monsters in range and restore missing wrath.
3) Condemn for good burst damage (better with a 2-hand weapon, preferably) while the monsters are all locked in place near you.
4) Spam Blessed Hammer [Burning Wrath] to clean up.
Hope this helps answer some of your initial questions, and gets you on the right track! Once you're used to the class more, you'll have a better idea of what kind of build to use at max level.
Feel free to ask if you have any more questions, etc.