Composers make a living nowadays, the same way that they did 500 years ago. People with money to burn hire a composer to write for them for a particular occassion e.g. royalty and nobility would usually have a court composer who would write music especially for parties and the like. Composers would often teach music as an everyday job (to pay the bills), again royalty and nobility would have a court composer who would teach them music and write music for them to play in lessons. Finally, some composers were also performers, they’d be hired on to play music as well as write it at times.
Nowadays it’s much the same. Major companies hire a composer to write for a film, theatre production, radio or TV show etc. Composers would often teach music as a sideline job to pay bills and more often than not would perform other people’s music as well to help earn an extra bit of cash.
Some composers even have a regular 9 to 5 job to pay their bills. I work in a studio as my day to day job, a friend of mine works in a petrol station and another composer friend is a manager in a hotel. It all depends on your situation.
Not much has changed for composers except for the technology around them.
some or most i would say, have students and a handful freelances in orchestras or otherwise..
Some worked for churches, like Bach did. Some composed because they were rich and they wanted to compose, like Gesualdo.
Many -I’d venture to say most- also gave lessons both in composing and in playing instruments. Another way they would have made money was looking to see who wanted music for something. For example, some plays require incidental music.
Some weren’t full-time composers. Charles Ives had a comfortable life as an insurance salesman and he also composed.