To be OP on your Minecraft server, you have a few methods.

1) Enter an OP command in the console of your manager

Enter the command from the panel :

op NICKNAME

2) Enter the command from the game; an OP can gives the OP right to another player

Any OP player can give the same right or deop another player with two simple commands :

/op NICKNAME: gives the OP status to a player
/deop NICKNAME: delete the OP status to a player

Need advanced rights? Switch to a permissions system.

If you wish an complex permissions system such as PermissionsBukkit, GroupManager or PermissionsEx is more complicated as it's based on groups.