2D and 3D RNAV Approaches
There two types of approaches according to the ICAO, those that offer only lateral navigation performance (2 dimensional) and those that offer both lateral and vertical navigation performance (3 dimensional). 2D GNSS are non-precision approaches (NPA). For example, LNAV and LP. 3D GNSS approaches are APV approaches. For example, LPV and LNAV/VNAV.
What RNAV Landing Minima to Use
In order to know what landing minima to use for your GNSS approach you need to know the capabilities of the GNSS equipment installed in your plane. In order to make use of APVs in North America you will need a navigation unit that supports WAAS (or Baro-VNAV). If you do not know what unit is installed in your airplane the approach minima should be displayed on your GPS unit as you intercept the approach course. An explanation table from Transport Canada gives a further explanation of RNP for specific approach minima.
Example RNAV Performance
LPV and LNAV
Here is the RNAV (GNSS) Z RWY 07 at CYXX Abbotsford, BC. As you can see there are 4 sets of minima; LPV, LNAV/VNAV, LNAV, and CIRCLING. Depending on the navigation performance you achieve the landing minima change. For example if you are getting LPV performance you can fly the approach down to the DA of 417 ft ASL before you must initiate a missed approach if you do not have the required visual reference. If you are getting LNAV performance you can only fly the approach down to the MDA of 760 ft ASL before you must initiate a missed approach. (See the landing minima visual reference requirements below from the CAP GEN.)