For most Android tablets you will need to install an app to unzip files, click on the icon to get one without any cost:
Once the download of your file is complete, open the Easy Unrar app and click on 'download', where you will find the downloaded audiobook. Click on the zip file, then 'Extract', top left of Unrar app.
If you are for example on an Amazon fire tablet you can only play music from the Amazon store, so you will need to install a separate music player. This is probably a good option for any android tablet. Click on the icon on the right to get this wonderful music player.
Open the VLC music player and click on 'directories' and then the 'download' folder, where you will find the audiobook mp3 files.
Next to the first file on the right you will see three vertical dots, click on them and choose 'Play all' or 'Add to playlist' and begin listening.