Saving data MySQL PHP

I am trying to save some data from my website to my database. This works on both my local machine and thorugh my student host:

some php…

$connection = @mysqli_connect('localhost', 'username', 'pw') 
    or die (mysqli_error()); 
mysqli_select_db($connection, 'mydatabase') 
    or die (mysqli_error()); 

some php…

I have followed all the instruction from: https://www.digitalocean.com/community/articles/how-to-install-linux-apache-mysql-php-lamp-stack-on-ubuntu

and

https://www.digitalocean.com/community/articles/how-to-install-and-secure-phpmyadmin-on-ubuntu-12-04

So i have php and mysql installed and I can access my databases through phpmyadmin

I still can’t save data to the database through my website using the script listed above.

Any idea what might be the problem?