Dear Sarada!

I reccomend QGIS - among the best in open source GIS.

Download http://www.qgis.org/en/site/

Documentation http://www.qgis.org/en/docs/index.html (see for 2.8 version)

Also, you can see http://www.saga-gis.org/en/index.html and https://grass.osgeo.org/ - good free GIS.

I also recommend QGIS. In addition to Sergey's links, I can add that there are tutorials and training materials available: http://www.qgistutorials.com/en/

https://qgis.org/en/site/forusers/trainingmaterial/

you can find other tutorials on youtube,

and there is a very active and helpful user list https://lists.osgeo.org/listinfo/qgis-user

Thank you Sergey Bolshakov and Roderick B. Salisbury for your suggestion.