A proofread corrects typos and overlooked errors in grammar, punctuation, capitalization, etc. No big changes are made at this stage. It’s your last minute check because no edit ever catches everything and because you may have accidentally introduced errors while making changes after one of the other types of edits.
At this time, I no longer personally do copy edits, but my husband does. He writes a weekly grammar column for my blog if you’d like to learn more about him and what he can do for you. You can also contact him through his website at https://saylorediting.wordpress.com, or you can email him to talk about rates and availability at christopher.saylor21 [at] gmail.com.