For example, what patent should I apply for when applying a speaker to a bicycle? Is it a utility model patent or an invention patent?

First of all, this is a new practical patent, whether it is a bicycle or a horn on a bicycle. Before that, "bicycle" and "horn" had existed subjectively. Your ability is different in application or use. So we should apply for a new practical patent.

The steps of patent application should be that the law firm licensed by the state and authorized by the patentee submits the patent application to the Patent Office.

After a patent is approved, it shall be submitted to a law firm to safeguard the legitimate rights and interests of the patent. However, commission is indispensable. At present, most licensed law firms are free of charge before applying for a patent as long as they accept it for you (but I work in a public institution. If it is an ordinary personal invention, it will definitely be charged before).

The application law firm will give you a framework document, just fill it out. PCT application and the State Patent Office can be applied at the same time.