To find free 'ringtones' for your phone, you can use the free
tonos gratis app. This application lists the songs stored on your device and has a search bar on top. However, you won't be able to search for newly downloaded songs with this app, and you will have to use the restart button to fix that. This app can be used to trim a song into smaller parts and select a section of the song.
To create a ringtone, you can use an app such as GarageBand, which loads a song into its first track. Click on the yellow Record button and cycle through the tracks. Most Android 'ringtones' run as 30-second loops. For best results, you should record an mp3 file that's at least 30 seconds long. If you're unable to record your own ringtone, use the free application to download an existing 'ringtone.'