A musician can make money in many ways. It depends on whether you are a performer, an educator or a content creator (of music, lyrics, and reviews).
As a performer, the first and most obvious way is by performing. You can play solo or in a group for concerts and festivals. Many performers are also teaching workshops and short courses in 'spare' time.
As a music educator or private studio teachers, the majority income will come from regular music lessons; and sometimes through project-based services such as curriculum development and jury duty.
For content creators who composes music and text, you will mainly get paid by licensing your music for films, TV, commercials or even video games.
No matter what your main role is, you can expand your career through networking and collaboration. Invite other musicians to work with you for your next project and you will likely get an invitation one day!