An editor helps and supports the Mangaka by ensuring that the Manga is being produced at an even pace and that deadlines are met. Editor may also do a little bit of managing of the appearances of the Mangaka. He or she will often comment on the layout of the manga panels, the art, and make sure that the manga stays up to company standards.
They also do basic editing and story suggestions of the manga itself. The influence of the editor can range from manga to manga and project to project as both the mangaka and the company allows. Generally they are considered the boss of the mangaka and oversee the majority of the production to make sure it runs smoothly.
In addition, in cases where the mangaka cannot supervise the anime character and action figure designs, the editor often goes to supervise these things in place of the actual mangaka.
In the Weekly Shonen Jump unit, there are groups of editors led by a captain, also an editor. Above them are the Editor-in-Chief and the Assistant Editor-in-Chief, who aren't editors but they still keep JUMP running.
At a serialization meeting, the captains and the Assistant-Editor-in-Chief and Editor-in-Chief sit in to discuss what manga gets serialized, using a "yes or no" format to decide.