You and your book will be assigned to an editor who will steer you through the production process and be your main point of contact with the company. At least one person is now going to read your book very closely and ask you questions and make comments about it. There are likely to be two levels of queries and they may come from two different people.
Broadly speaking: A commissioning editor, senior editor or project editor cares about the structure and content of the book. She will tell you that the action takes too long to get going and you should drop. So you may be asked to add, subtract, rewrite or shuffle. (With fiction this is likely to happen before they offer to publish, but even so you should be prepared for further suggestions.)
A copy editor, line editor or desk editor (who in many cases will be a freelancer employed on a project-by-project basis) cares about consistency, spelling, grammar, punctuation and repetition. Her job is to notice that you spell ‘organisation’ with an s but ‘realize’ with a z, or that you have told that anecdote about your heroine’s first day at work three times. A lot of this will seem like nitpicking, but that is what a copy editor is paid for. Good publishers believe in ‘getting it right’ and that includes putting the apostrophes in the right place and not saying ‘imply’ when you mean ‘infer’.