First of all, let's read
http://en.wikipedia.org/wiki/File_system_permissions
to get more information about permissions.

Yes, We acknowledge there are some omissions in the installer text but I will rewrite all these.

Generally, we are waiting for the read+write access for several folders to keep files in it,
for ffmpeg.exe we need to have executable permissions only (not read-write)
And for several files we need read-write as well.