While translation is fairly self-explanatory, there is frequently a great deal of confusion between proofreading and the various levels of editing and copy-editing. Here is a short explainer:
Proofreading consists of checking the “proofs” of a copy-edited text for errors before publication. This service is cheapest.
Copy-editing refers to getting your text into shape so that it is ready for publication. A useful explanation of the differences between proofreading and copy-editing can be found here. Copy-editing may also include making stylistic changes or interventions.
Finally, there are more substantial forms of editing, such as line-editing and developmental editing. These involve making structural, substantive changes to a manuscript, including, yet often going beyond, questions of style and author voice. These tasks are the most demanding.