Edit draft from other author

Please review the information here: http://codex.wordpress.org/Roles_and_Capabilities
Specifically, the following:

Editor – somebody who can publish and manage posts including the posts
of other users.

An Editor is exactly that – someone who can edit what other people are doing.

Ensure that the Users who you want to have Editor rights are assigned as Editors in the Users menu.

If this doesn’t answer the question, please revise your question with more information and perhaps this may also help understand a bit more: Allow Editors to edit pending posts but not draft ones