PlayingSTO, when choosing your bridge officers, pay close attention to their ability lists. You do not want to duplicate abilities between your bridge officers if you can avoid it. You can customize the appearance of each bridge officer once, for free. You can also rename them once, for free. After that it costs energy.

Your first few missions will award you with three bridge officers. Periodically after that you'll have the opportunity to pick up another. You can also purchase them using starfleet merit. You must promote your bridge officers to gain access to their more advanced abilities. In order to promote them, you need to have spent a minimum amount of skill(star trek online credits) points on them first. You also must be one rank higher than the rank you are promoting them to, so, you have to be a lieutenant commander to promote a bridge officer to lieutenant. You can see the requirements to promote them by hitting the promote button on their character page.

Bridge officers will use any available ability on the ground. In space, their abilities are limited by the ship type and the station they're assigned to. For example, they can only use lieutenant powers if they're at a lieutenant station. In addition, here is the cheapest STO powerleveling service.