In STO, all Bridge Officers have the potential to learn 8 skills, four grounds and four spaces, one of each per rank. On the ground the skills are pulled from the same pool as the skills in your captain kits.
While ground officers always have access to all the skills star trek credits available to their rank on the ground. An ensign has one ground skill; a lieutenant has two, and so on. On the ground you will always be in a group of five. Every spot not occupied by a Captain is filled by one of the group member's Bridge Officers. Five players means no Bridge officers, four players means one Bridge Officer, three players means two Bridge Officers and two players means three Bridge Officers. One player, or solo play, means four Bridge Officers. That is where we will focus.
In a group you generally want a healer, a support and 3 DPS classes. Anyone, with a good gun equipped or with Martial Arts, can do DPS. You'd better use a second Tactical or Engineering Officer focused specifically on DPS. Tactical officers get powers and abilities that do damage, such as Grenades, martial arts moves or damage buffs and debuffs. They also have access to threat generating abilities like draw fire. Also here are star trek online credits.