Health, Mana, Energy: all characters have a health bar which shows you how much life force you have. Deplete the bar, and–well, every video gamer from the dawn of time can answer that one. You're sleeping with the fishes. Your character will also have a Mana bar, if he or she is of the Cleric or Magic calling, or an Energy bar if you're rolling either a Rogue or a Warrior. Mana and Energy provide the resource for most of your abilities.
That light blue bar below the other two is your Charge. Charge is built up through the use of some abilities, and then spent on others. Reading the tooltips of your abilities will help you determine which skills create the resource and which skills you can blow it on. Running around with a full Charge bar is silly, not to mention a waste of dps, threat or healing. You can't cash it in for chocolate, so you might as well use it.
You have eight basic attributes: Intelligence, Dexterity, Valor, Armor, Strength, Wisdom, Endurance and Toughness. Intelligence gives you Spell Power, Spell Crit and increases your maximum Mana, if you're into that sort of Mana-based dps thing. If you're more of a healer than a fighter, you'll want to look for Wisdom. That provides healing Spell Crit and Mana Regeneration. Endurance and Armor are similar in that Endurance provides a bigger Health pool, allowing you to take more damage before you die. Armor reduces the amount of damage that gets through to you, allowing you to stand and fight for a longer period of time.
Focus and Hit are similar to each other in that Focus reduces your target's chance to resist your spells while Hit reduces the chance that your target can avoid your physical damage. Short answer: melee needs Hit, while casters will want Focus.
Melee dps will also want Attack Power and Physical Crit, both of which are provided by boosting your Strength. Strength will also provide some Block and Parry, making it, along with the Toughness attribute which reduces your chance to be critically hit, a primary Tanking stat. Melee users who are not tanking will probably want to invest in Dexterity more than Strength, as that provides some Physical Crit along with Dodge and Parry.
Finally, there's Valor, the PvP attribute. This only reduces the chance of incoming critical strikes, so you will still need all other stats required for you to function in PvE. Valor just helps to keep you from taking a huge Crit to the face from a member of the opposing faction.
Who Needs What?
Well, that's the big question, isn't it? The problem is that in Rift, with its system of three souls per role and huge amounts of crossover between tanking, healing and dps toons, there doesn't seem to be a hard-and-fast rule. Instead, players are given a bit more freedom to spec how they want and then look for stats on gear that supports their individual play styles.
For instance, if your Necro-Warlock-Dom likes to pop into a Chloro role and heal now and then, you can either gear her up with a combination of Int and Wisdom gear, or you can keep two sets to switch between. If your Cleric is a bit of a control freak and insists on either healing or tanking, you will definitely want two complete sets of gear. One set will consist of Wisdom and Int, while the other will be heavy on Strength, Toughness and avoidance stats.
In short, the attributes you favor will have more to do with how you like to play that what you are playing. And that is probably where Rift breaks away from those it imitates and comes into its own.