How to get public directory?

Use public_path()

For reference:

// Path to the project's root folder    
echo base_path();

// Path to the 'app' folder    
echo app_path();        

// Path to the 'public' folder    
echo public_path();

// Path to the 'storage' folder    
echo storage_path();

// Path to the 'storage/app' folder    
echo storage_path('app');