GPS Enroute will permit you do use an approved TSO GPS as the primary means of navigation in the enroute phase.
A GPS Arrival endorsement (DME/GPS Arrival) will permit you to carry out GPS/DME Arrivals using an approved TSO GPS.
A GNSS RNAV NPA endorsement will permit you to conduct said approaches, once again, using an approved TSO GPS.
Don't think that because you have the top two, you can go and conduct RNAV approaches. Very dangerous thinking, as without thorough understanding of the RNAV approaches, you can kill yourself.
morno