There is no big difference between Mysql and Mysqli. Mysqli is nothing but an improved extension of Mysql which supports OOP. mysqli extension allows you to access the functionality provided by MySQL 4.1 and above. In some blogs and benchmark says that Mysql is slightly faster than the Mysqli Extension.
MySQL is an RDBMS that runs as a server and provides multi-user access to multiple databases; MySQLi is an extension of MySQL.
2. MySQL does not need GUI tools in order to administer databases or manage the data therein; MySQLi builds upon the features of MySQL and include object oriented interface, support for previously prepared statements, and enhanced embedded server support.