Initialise the Extension
To use the analytics service you must pass in your Flurry keys that you created through the Flurry website and a configuration instance to set various configuration options (FlurryAnalyticsConfig). 
var config:FlurryAnalyticsConfig = new FlurryAnalyticsConfig()
        .setLogEnabled(true)
        .setCrashReportingEnabled(true)
        .setSessionContinueSeconds( 6 )
;
Flurry.service.analytics.initialise( "FLURRY_KEY", config );
(If you don't supply a configuration then the defaults will be used).
If you are cross compiling both iOS and Android you can use the initialiseWithKeys function to initialise both platforms.
Flurry.service.analytics.initialiseWithKeys( 
    "IOS_FLURRY_KEY", 
    "ANDROID_FLURRY_KEY", 
    config
);