Which iso can i download from
https://www.debian.org/CD/http-ftp/#stable
arm64 or armel ?
And dd the iso into my sd card to install os into raspberry pi?
That will not work for several reasons - the Pi is a 32 bit machine and has a unique kernel image and boot system.
The standard Raspbian image is based on Debian stable. You can always download packages not in the image from the Raspbian repository.
It is possible to run "real" Debian on a Raspberry Pi2 , but it involves some work since it is not fully supported in Debian wheezy or jessie :