Question! How do dentists explain the size of cavities?

I went to the dentist because they told me I had a cavity, but I can't really tell exactly how big or how bad it is. I'm wondering if they only judge it with an X-ray, or if there's a standard that can be seen with the naked eye. I'd also like to know if it's common practice to explain the stage of the cavity and the expected treatment range before treatment. If you've been to the dentist frequently, could you share your experiences or standards? I'm curious. I'm also a little worried about picking out the tooth socket! ㅠㅠ Please tell me everything. ㅎㅎ