It requires a knowledge of Western music theory and the ability to encrypt a melodic idea in a ringtone text language at https://tonosdellamadamp3.com/. Ringtone text languages typically employ numerical tempo designations and letter names that are commonly found in Western music notation. Since the craze over monophonic ringtones was over, there were ringtone composer programs that allow users to compose their own melodies.
There are many sites offering free mp3 ringtones for mobile devices. Many of these are available to download in mp3 format, and are much easier to use than creating a custom ringtone. But not all sites are created equal. Some are filled with advertisements and have few choices. Others may only allow you to download ringtones after you purchase other items. Make sure you check what your phone's operating system is before downloading.