Hi,
you have to send commands in CLI syntax via SSH. Maybe this helps:
http://wiki.mikrotik.com/wiki/User_Manager/PPP_Example
You might also want to try out the API - if supported (shameless forum search & paste)
http://wiki.mikrotik.com/wiki/Manual:API
http://forum.mikrotik.com/t/how-i-get-username-actual-profile-from-userman-using-php/77773/1