Download flutter from FLUTTER
or clone from master git clone -b master https://github.com/flutter/flutter.git
So, the flutter sdk path is where you copied or cloned the code till the C:\whateverDrive\flutter inside bin there is a file flutter so when coming to choosing SDK, please select the folder till flutter and add the same in env variable in your windows. remember to add the path till bin that is enough.
configuring the flutter sdk in android studio follow this carefully. This explains everything. ;)