The EW and NS bands correspond to the projection of the 2D displacement field measured, along the EW and NS directions. Values are given in meters, positive in the North and East directions. If at a point you have NS = -10 and EW = 0, it means the ground at this location moved 10m toward the South between the 2 acquisition dates (considering no other bias exists, such as topo bias, undulation from satellite roll/pitch, outliers from decorrelation, etc..), and neglecting the noise...
If you measure EW = 10 and NS = 10, the ground moved by 10*sqrt(2) = 14.14 meters, in the E-NE direction.
When you use the vector field tool, it is advised to first "clean" the correlation data. You can discard most of the outliers by thresholding the NS and EW bands to remove nonphysically large values, or values with low SNR (in practice, discard values with SNR < 0.9).
You may also need to destripe the correlation data, if undulation from satellite wobbling are present. When you display the vector field, adjust the parameters to obtain a good visualization (scale, smoothing, sampling). You can save the vector field as an ENVI layer (File -> Save as -> ENVI layer). You will be asked for projection parameters. You should input the projection parameters of your correlation file by clicking on "Change Proj...". You will have to select the UTM projection with WGS-84 datum, units in meters, and input the appropriate UTM zone (same as your ortho-images). Then you will be able to display the vector field on top of your ortho-images. When you open your ortho-image in a display, go to Overlay -> Vectors, and select the vector file you just created. Adjust color, etc.. to your liking for better visualization.
You should be able to find similar information in the COSI-Corr manual. Pls refer to ENVI user's guide for non-COSI-Corr functions.
Hope this help,