Step 1: Adding your OGG File

If you want to add new sounds or music, you will need a .ogg file. You can use any software or converter online to take care of this if you have an .mp3 file instead.

All you need to do is put your .ogg file in a secounds folder inside of the minecraft directory like so;

📁resource_pack
└── 📁assets
          └── 📁minecraft
                    └── 📁sounds
                              └── 📁custom
                                        └── 📑arcade_music.ogg

Step 2: Reading New Sounds

Once your .ogg file is in the pack, you need to make sure the pack is able to read the file. For this you will need to create a sounds.json file and place it inside your minecraft directory like so;

📁resource_pack
└── 📁assets
          └── 📁minecraft
                    └── 📑sounds.json

Inside of your sounds.json you will create something like this;

{
  "custom.arcade_music": {
    "sounds": [
      "custom/arcade_music"
    ]
  }
}

Step 3: Result

Your sound is now implemented and ready to use in game. To play your sound, use the following command:

/playsound minecraft:custom.arcade_music master @p

You can replace the sound name with whatever you specified for your sound name in the sounds.json file.