As a group you will also be required to create a regiment as well. Regiments give basic stats for each character as well as additional roleplaying elements that would determine how your group will be deployed and what equipment and vehicles you will have access to before you enter a mission. This will require your group select a Homeworld you all hail from, as well as your commanding officer that leads your regiment and their personality, and lastly the doctrine(s) your regiment follows in combat.
For our campaign you will need to create a backstory, it may only be a few paragraphs and you don't need to be the best writer in the world, but it is needed to help develop your place in this campaign and also set the mood of how your character would handle the situations, because remember, its NOT you, so every action or reaction may not be the way you personally would handle it. I will be listing information below about the planet you come from and please visit the Regiment info page and 40k history to learn more about the universe and how to shape your character. The timeline is 20 years after the Black Crusade was finally over on Cadia, year 032.M42. Your age will be within 16-25 and you can choose male or female (game mechanics no difference for either.)