Not too sure of your knowledge so will simplify things for you (not being condescending though
)
To be 'capped' is to reach the certain stat level where it is exactly what you need, so you have 'capped it'
main things for a melée class (which rogues are) are to be "hit capped" which means stacking hit on your armor until you jut cap. Being capped in hut means none of your attacks will ever miss.
Next for melée class is "expertise cap" capping this stat guarantees that none of your attacks can de dodged/blocked or parried.
Becoming hit/expertise capped is essential as a melée class as all your auto attacks (basically thise are the attacks your toon auto does when you aren't using an ability) will never miss and they are a good boost to your dps (damage per second, how your performance is measured the higher the better.) get these capped and your dps will noticeably increase.
Now not wanting to insult your intelligence here but if you are playing rogue make sure you stand behind whatever you are attacking where possible. This too will boost your dps, I die a little everytime I see a rogue stood infront of an enemy.
Anyway back on topic your best bet to find out what % you need to be hit capped and what expertise rating you need (you can see your current stats on the side of your character info screen) is to go to the wow Europe site, go the rogue sub section of the forums and ask. Someone will know. Then make it your goal to keep these two stats capped. I would then recomend haste but I'm nit too hot on current rogue specs.
Apologies if anything I have said was really obvious and insults your intelligence, just found it easier to give you the simplest explanation so you don't feel lost
good luck!
