[AC Question]

I want to save my music to the music app my phone came with. But I don't know how to upload my music to the cloud, then to the app.

[SpookDroid]

Well, it depends on which cloud service you use. The stock music player can only read/play music files that are actually saved in your phone, not directly from the cloud (streaming). So to save those files to your phone from a cloud service, it depends on which one you're using and their app to figure out how to save files from your cloud back up to your phone (most have a pretty straight forward SAVE button, but some don't let you do this for multiple files at once, making it a PITA).

Some 3rd party music players, however, will let you connect a cloud storage account (Dropbox, Google Drive, etc.) and stream directly from there.

If you choose to upload those to Google Play, then using the Play Music app you can access those files for streaming or if you choose, you can download the files or playlists you choose for offline listening.