Copy Editing is when someone reviews your work for punctuation and grammatical errors. They are examining your sentence structure to correct spelling errors, fix punctuation mistakes, point out inconsistencies in verb tense, whether you've used the words "lay" or laid", “to” or “too”, “rather” or “whether” properly, etc. A copy editor can also examine and determine whether your paragraphs are too long. A good copy editor can also assist you with making your writings easier for the readers to understand.
Content editing is when someone reviews your work, from an overall perspective to make sure your story is well written. They are looking to see if your story has an attention grabbing introduction and a good conclusion. A content editor is looking for places where your story may fall short. Are your characters believable or are they poorly developed? Do you have too many characters that look and sound the same? A good content editor looks to see if there is enough emotion in the scenes and if you used enough descriptions throughout your story. They also want to know if your reader would get bored.
Whether it is a Content editor or a Copy editor, they would provide you with a summary or outline showing your errors or any inconsistencies they’ve come across. For copy editors the summary may provide suggestions for sentence structure, word play and grammar or dialect fixes. For content editors that summary can contain suggestions for re-writes, things that should be moved around, deleted, or sections that need more details added to it. However, it’s up to you as the writer, whether or not you want take their advice.
When taking advice from others it’s always good to look at things from various perspectives to ensure the message in your writing project is being expressed the way you envision it.