What he meant was that the student must ultimately teach themself. The great Hungarian composer Béla Bartók always maintained that music composition cannot be taught (even when he was teaching it himself!). You might want to read a few books on music production and the music industry in general. If you are a singer/songwriter you would usually hire a studio and recording engineers to record your music - although of course dance music and similar styles can be produced using nothing more than a laptop with appropriate programs on.

So I should make it clear that it's very rare for one person to write, perform and produce their music as it's such an enormous operation. Many of these are never recorded I remember being told as an undergrad that only something like 40 per cent of songs written get recorded and of those only about 10 per cent get more than one radio play), another person who will make backing arrangements, an army of engineers who will record and produce the music, and another army or agents, fixers, managers, and marketers who try to make the record commercially successful. There will be somebody else who writes the songs (not necessarily even in collaboration with the artist the major record companies have huge libraries of songs in storage which can be pulled off the shelf for new artists to perform.

They simply sing or play instruments and are the 'big name' on stage. Although there are plenty of people who write, record and perform their songs themselves (and even, thanks to the internet, market and distribute the records too), most performers are just that, only performers. The long answer is a bit more complicated and it will necessary to explain a little about how the music industry works. Then they get on stage and play and hopefully everyone buys their records. A very large number of rock and pop musicians, including some of the most famous, cannot read music and simply write their songs (if they are songwriters as well) down by working out the melody on an instrument and memorising it.

How to make music without instruments