The Meaning of the testimony, Muhammadar- Rasoolullah.
It is to affirm inwardly and outwardly that he is a slave of Allah and His Messenger to all people, and to act in accordance to it's requirements which are:
a) Obedience to the Prophet in everything that he orders
b) Believing in everything he has informed us about
c) Refraining from everything that he has prohibited d) Not to worship Allah except in the way he has prescribed.