There are thousands of tunes available on the Internet in the form of computer files of various kinds and which can be an alternative to printed sheet music for musicians. Traditional instrumental music is particularly well supported because there are no copyright problems.
The easiest to use are simple graphics files of the sheet music itself which can be read from the screen or printed. However, the largest amount of tune data is available in files of other kinds which can be converted to sheet music with suitable software, but better still can also be played audibly.
The most common such files are MIDI files which many computer users are familiar with, and can be listened to using only easily available software such as that built into Windows. Another particularly useful file format is ABC. These files are extremely compact and so huge numbers of tunes can be stored in only a small amount of disc space.
As a general principle, the more compact the data format is, the larger is the amount of data available, but also such formats are more demanding of technical knowledge and special software. However it is not too technically difficult to obtain tunes in this form, to be able to listen to the tunes, and to convert them to sheet music.
For further details, and information how to do this, and sources of tune data, see the sound technology page by the same author:
www.technology1.co.uk/sound.html