I'm not sure exactly what kind of TIF format a LISS3 image is, but I will assume that it is a geoTIFF as this is the case for most satellite data. Whitebox GAT can import uncompressed, single band GeoTIFF images simply by selecting them from the list of available files when you press 'Add Layer'. You can open multiple images at a time as well:
Whitebox will automatically convert the TIFF image into its own native raster format (.dep header with .tas binary data) but will issue a warning so the user knows what is about to happen:
You can just dismiss that warning. When the image is first displayed, you may find that it doesn't look quite right because it will default the display minimum and maximum values to that of the image min and max, which may not be very appropriate. You can change the display minimum and maximum values in the Layer Properties dialog:
(Clipping them by a specified percent is quite effective) and it will re-stretch the palette. You may also want to update the image NoData value (under the File tab of the Layer's Display Properties).
Alternatively, you can improve your image using any of the several image stretches available within the Image Processing Tools => Image Enhancement toolbox. There is also a tutorial in the Help called 'How To Get Data Into Whitebox' that might be of help.
Please note that I am the lead developer of the Whitebox Geospatial Analysis Tools project.