Macro's are key combinations (like pressing ctrl and 1 at the same time) that are used as shortcuts for long commands. You can use them to cast spells you use often, or use abilities you use often. They get kinda complicated in how they're worded, so check out the guide here at Allakhazam. (Guides section's at the far bottom of the left column)
Also, it would be best to know a few of the shorthand terms people use in game. You might know some from chatrooms/AIM/etc, those like AFK (Away from keyboard), BRB (Be right back), and such.
Some other terms are unique to MMORPGs. The "Zone" is the area you're currently in. If someone tells you "to Zone", though, they mean run to the nearest boundry between zones. (Monsters can't pass between zones)
I'd also suggest looking up information of the different classes, and choosing one before you start playing. Make sure it loosely fits your race of choice, though you're allowed to choose any combination. (Galka White Mages really are hard to play) Remember, you can change your class, but not your race (short of making a new character). If you know you want to cast spells, Galkans aren't the best choice. If you want to beat the **** out of anything you see, being a Tarutaru might be hard.
And most of all, no matter what anyone tells you, HAVE FUN! You're paying to play the game, so don't get into the habit of doing something just because someone tells you it's the way something's done. Experiment, and find they way that fits you best.