What's best exercises .speciffically dumbells for this muscle.thanks?

Close-grip Bench Press will workout your front delts, inner chest, and triceps. (Which are all used in boxing I believe)

Arnold Shoulder Press- Sit on a bench with your back rested. Take 2 dumbells. With your wrists/palms facing you extend your arms towards the ceiling and rotate your palms 180 degrees. This will hit your anterior, posterior, and medial all in one workout.

Anterior only- Front extensions (usually with small weights)- Stand up with your arms at your side. Extend your arm with a very slight bend in your elbow (just past parallel to the floor).