Find your servers my.cnf or my.ini file and look for the configuration statement skip-innodb in the [mysqld] section of your server. If it is in there, remove it.
In place of skip-innodb put in the following configuration statements.
innodb
innodb_file_per_table = 1
innodb_flush_log_at_trx_commit = 2
This is just a minimal setup for testing and is not suitable for performance. See the rest of the tutorial for more informastion on performance.
Restart your server. It will create new ibdata1, ib_logfile0 an ib_logfile1 files and put appropriate messages in your log. After the server completes startup, SHOW ENGINES lists InnoDB as "YES".