A manuscript assessment is a detailed, objective report on your writing project. It notes strengths and weaknesses, and offers suggestions on how to rework your manuscript towards a publishable form.
A novel assessment comments on characterisation, style, dialogue, and validity and impact of narrative.
Friends and family can be encouraging. They might even be able to tell you what they like and don't like about your work. But they can rarely give you a professional writer's detached feedback to help you learn and improve.
Writing is mostly hard work and determination. Talent helps, but it's often those who are willing to work and re-work their writing who are successful. Publishers and editors these days are inundated with unsolicited manuscripts. An assessment gives you a better chance to get their attention by making your work as good as it can be.