I am a novice FSLNets user trying to utilize it for our ICA data.

Would you kindly explain/elaborate on :

%%% you must have already run the following (outside MATLAB), to create summary pictures of the maps in the NIFTI file:
   %%% slices_summary <group_maps> 4 $FSLDIR/data/standard/MNI152_T1_2mm <group_maps>.sum

What dataset this refers to and does it have to be saved with '.sum' extension?

Thanks!
Inna