Damselfish are often used as tank starters as they can bring biological stabilization to a tank quickly. Be careful, however, when adding new fish. Their aggression and territorialism are not limited to their own species. Your starter Damsels may not take kindly to having their tank space encroached upon by new additions.
Damselfish are far from picky when it comes to food. Many adapt easily to flake food, but a good diet should include meat and vegetation. One favorite treat is a leaf of Romaine lettuce dropped into the cage a couple times a week.