Your character's reasons for becoming an adventurer with this particular group may be as many as the stars in the night sky, or as singular as a solitary atom within a vacuum. No matter the number of reasons, it is important for you as player to understand what those reason are and why they are important to your character. The reasons for becoming an adventurer may seem insignificant to you (the player), but to your character they could mean the difference between life and death.
Is your character seeking fortune and fame?
Are the seeking our magic and power?
Was their one true love kidnapped by a band of space pirates and the only way to save them is to become a pirate yourself?
Or has a vampire been terrorizing your country and you have joined an adventuring party in order to put an end to his evil influence and terrorism?
Whatever your character's reasons are for becoming an adventurer, makes sure to discuss those reasons with your DM/GM to see how they might be able to incorporate some of those reasons into the game's storyline. When a character sees their reasoning(s) being played out in the game before them, all of a sudden the adventure becomes even more personal for them, thus allowing you (the player) to enjoy the game even more.