here are 4 ways to add a frame to a mirror - https://www.charlestoncrafted.com/2018/03/20/four-best-ways-frame-mirror/
If you are talking about actually making the mirror glass itself you won’t be able to do it yourself. They are made in factories under very strict conditions. It also requires some specialized chemicals such as silver nitrate which is super expensive and is not normally sold in small quantities.
I would need a wee bit more info before I could even attempt to answer your question.