Hi there Mouhamed88
You can buy the $10 Add On which will top you up with extra data (see, http://www.boost.com.au/rates), or you can recharge.
You cannot use the Telstra 24x7 App to track you data usage, that only works for a Telstra service. You however are able to see how much data you have remaining by using the USSD service - #111# on your handset. Or you can navigate to http://care.boost.com.au on your phone's web browser to view the same information (make sure Wi-Fi is disabled when trying to access your account details).
Hope this helps.