Open git bash and execute
ssh-keygen -t rsa -b 4096 -C "[email protected]"
This procedure generates two files: .ssh/id_rsa and .ssh/id_rsa.pub. Add public key to Github.
Use puttygen to convert the private key (id_rsa) to ppk (id_rsa.ppk). Save this new private key, and execute:
pageant.exe .\.ssh\id_rsa.ppk