Please be a bit more precise regarding terminology. This helps us understand your problem. Give examples on specific terms and where you read them (normalized radar, polarized coefficient, integral equation model,…) We can’t know what you’re working on 
I’ll start here:
How can i join two SAR images together ? What is the process?
Are the images next to each other or cover the same area?
if i have a shapefile , how do i use it to subset and get the correct study area ?
this is answered here: Subset using Vector file - #2 by marpet