There are many forms of meditation. One form is guided meditation.
In a guided meditation, there will usually be an element that guides you through the meditation itself. This could be a person talking and guiding you, it could be a sound, or it could even be both.
Many guided meditations incorporate the element of sound. These sounds could be the sound of rain, rivers, wind, bells, or even music.
Sound is a useful element in meditation due to how easy it is to follow and stay focused on the sound.
This is especially helpful for beginners who are just starting out with meditation and find it difficult to sit and meditate for long and even short periods of time.
Many beginners and even more experienced meditators, incorporate sound and music into their meditations as it allows them to focus better and get into a meditative state faster.
It also helps in situations where it is difficult to find a quiet place. Putting on music or meditative sounds can reduce the background noise that would otherwise bother you, and allow you to follow the sounds and get into a meditative state.
There is no real limit to what sounds can be used. Just as meditation is a different experience for everyone, so can the sounds being used be different from person to person. Some people find it calming to meditate to the sound of a river stream, while others may prefer the sound of the wind blowing through the forest trees.
Other common sounds are calming acoustic instruments, and abstract sounds.
There is also no limit in terms of the origin of these sounds. If you live near a forest, a river, or any form of nature, it can be incredibly calming to have a meditation session in nature. If you do not have that option, then even putting on music or sounds on your phone is a great option.