In the UK a professor is generally a leading researcher recognised internationally & will generally have an extensive list of publications and partners (expectations will vary from university to university and field to field).
To be promoted generally both fellows within your institution & an external institutions will recommend the promotion. Im sure their is some lobbying & internal politics but this is something well above me.
The loose path is PhD, research fellow, lecturer/associate professor/various titles followed by professor. Professors generally are managing a group of researchers with other senior academics, postdocs & PhD students as well as routinely bringing in significant funding.
How long does it take? Depends how respected your work is, lots of people never get their, it’s fair to say most people give up before reaching that title.
Elsewhere in the world the title means different things, in the US the term just refers to a professional academic so a much lower bar, and not necessarily a researcher.