You correct minor errors in grammar, spelling, and punctuation during the editing and proofreading.
Proofreading refers to the final stage of the editing process, focusing on surface mistakes such as misspellings and errors in grammar and punctuation. You should proofread only after you have finished all of the other editing revisions of your piece of work.
Editing is the stage after you finished your first draft. You reread your draft to check the organization of the paper, to review if the transitions between paragraphs are smooth, and your evidence really supports your argument.