Lucy is a Celestial Mage. She makes contracts with spirits, and then is able to summon them in battle. Though she can also summon them outside of battle. She cares deeply for her spirits, and treats them as equals. This is not always the case for Celestial mages. This is why Lucy's bonds with her spirits are so strong.
[Edit]Lucy always dreamed of joining the guild Fairy Tail, but because it is one of the most popular guilds she wasn't sure she could. When she first meets Natsu Dragneel she doesn't realise that he is a member of Fairy Tail. She's tricked by 'Salamander' when he says that he can help her join the famous guild. Sure enough Natsu comes to save her, causing massive collateral damage in the process. He then offers to take her to Fairy Tail.
She quickly falls in love with the guild and all the members. She never goes on a mission by herself. Whenever she tries someone tags along, though Natsu always ropes her into helping him. She spends her free time writing a novel, and she loves literary art. Because of this Levy Macgarden becomes her close friend. She admires Erza Scarlet.
As mentioned earlier she always goes on quests with Natsu, and is later joined by Gray Fullbuster, and Erza Scarlet.