Hi @Ranjan07,
To mask out a product in SNAP using your AOI:
- Select your product on the product explorer
- Go to Vector -> Import -> ESRI Shapefile
- Navigate to your directory, select the shp and click ok (make sure your shp and image share the CRS)
- Go to Raster -> Mask -> Land/Sea Mask
- In the processing tab, select ‘Use vector as a mask’
- You can also uncheck the SRTM option
- Press Run and check results
You can definitely find out more info about this process in this forum. Check the link
http://forum.step.esa.int/search?q=clip
Hope it helps,
M