A cover version is a recording of a song that was written, performed and commercially released by another artist previously. That means if you record yourself singing the latest track by Ed Sheeran, that is a cover version.
To release a cover version, you need the necessary permission from the rights holder(s) - that means the writer/s of the original song or their publisher/s - and this is usually done by obtaining a mechanical license. 
In most cases, the music stores featuring your cover version will take care of this (woo hoo!), but if you wish to release your cover version for sale as a download in the USA, you will need do it yourself.
Don't worry, as long as you have not changed the lyrics or made significant changes to the melody or character of the original song, this can easily be done by purchasing a mechanical license from Harry Fox Agency (https://www.harryfox.com/), Loudr (https://loudr.fm/) or easysonglicensing (https://www.easysonglicensing.com/).
If you do not want to purchase a mechanical license and make your release available in the USA, simply de-select 'United States of America' in the release flow when creating your release.
If you release a cover, please click 'yes' when asked if your release contains a cover, sample or remix when creating your release. Then please contact our Customer Support team with the required documentation. After you have provided this, only then will your release be sent to stores.