Target specifies the movie clip to duplicate or remove. See Specifying targets. New Name is the instance name for the duplicated movie clip. Provide only the name, not a target path. Then, once named, the instance can be targeted from another action.
Depth determines how the duplicated movie clip appears when overlapping other objects.
Think of depth levels in terms of the stacking order with level 0 the initial level. Each successive duplicate movie clip needs to be given a depth, otherwise each duplicate will replace the previous clip at level 0. Duplicate movie clips are always on top of the original movie clip. Remove duplicate movie clip changes the statement to Remove Movie Clip. Duplicated movie clips do not disappear unless the parent movie clip disappears, or you use the Remove Movie Clip statement.