Some Tutorials for Beginners: 

Introduction to Vegetation Health Indices

https://www.youtube.com/watch?v=rxOMhQwApMc

Calculating Normalized Difference Water Index in QGIS (Open Source RS Software)

https://www.youtube.com/watch?v=y_Ah7Zv-o0k&t=46s

Calculating Normalized Difference Vegetation Index in QGIS (Open Source RS Software)

https://www.youtube.com/watch?v=vpxVkYaWMno

https://www.youtube.com/watch?v=SSDbFL0juyk

Sentinel - 2 from Sentinel Hub

https://www.youtube.com/watch?v=AkA0ya3A9lU

High-Resolution Alos Palsar DEM

https://www.youtube.com/watch?v=sJP5VuiL5aw

Earth Explorer

https://www.youtube.com/watch?v=Wn_G4fvitV8