To block access to a specific folder add a .htaccess file to that specific directory. The .htaccess file should contain the following line:
deny from all
If you would like to be the only one who have access to a specific folder you may password protect that folder. This will allow only users who have the correct password to access this directory.
To protect your folder, login your cPanel and navigate to „Password Protect Directories“. Select the directory which you would like to password protect and set the username and password which will be required to access the folder.