you can buy them on Starbase 1, in the Sol System; I forget the name of the character who sells them, but she's near the Admiral's office, I think (I know it begins with M, sorry). Follow the signs for personel. You can pick from a variety of races, and they each come with set abilities, but you can change them by buying new ones from the guy next to the lady who sells the BOs. They are both near Cmdr. Brat, who you need to find for one of the beginning quests. BOs and BO skills cost Starfleet merits, not credits, just fyi.