Copy your private key to ~/.ssh/
chmod a-r id_rsa
chmod u+r id_rsa
Permissions should read:
.ssh directory: 700 (drwx------)
public key (.pub file): 644 (-rw-r--r--)
private key ( id_rsa ): 600 (-rw-------)
To save the passphrase in the keychain type:
ssh-add -K ~/.ssh/id_rsa
Enter your passphrase.
To tell the ssh agent to use your key from the keychain, create the file ~/.ssh/config
and put this in it:
Host *
UseKeychain yes
AddKeysToAgent yes
IdentityFile ~/.ssh/your_id_rsa
IdentityFile ~/.ssh/your_id_rsa2 (if you have multiple)