Chmod which is fully known as change mode is a Linux/Unix shell command which is used to change permissions of files and directories.
In some web hosting environments, a user may need to use this command to change some file or directory permissions to make them writable by WordPress. If users don’t have access to a Unix shell.
There are times when you want to add a plugin from your WordPress dashboard, upgrade a plugin, add image, or something similar. sometimes based on your web hosting settings, you might not be able to do any of that because the file/folder permissions are not correct, then you would need to use the chmod.