Some people create their own sound. Some people use recorded sound clips, which are somewhat like graphical clip art. Sometimes, you'll hire a composer to create sounds for you. Depending on what type of sound you'd like to use, you may want a professional to create it for you. If you'd like to use music on your site, consider using a composer instead of creating it on your own.
Musicians have an ear for what type of music works with what.
But you can easily create feedback sounds or sound effects yourself. You can even tape record your dog barking for a unique sound effect. Creating sound yourself can be more economical than hiring a contractor or purchasing sounds from a sound disc, and it means your sounds are yours. You also need to think about whether you have the time to create sounds from scratch. But, purchasing sounds from a sound disc is similar to purchasing graphic clip art.