1. Start the ssh-agent in the background.
```
eval "$(ssh-agent -s)"
```
2. If you're using macOS Sierra 10.12.2 or later, you will need to modify your ~/.ssh/config file to automatically load keys into the ssh-agent and store passphrases in your keychain.
```
Host *
AddKeysToAgent yes
UseKeychain yes
IdentityFile ~/.ssh/id_rsa
```
3. Add your SSH private key to the ssh-agent and store your passphrase in the keychain. If you created your key with a different name, or if you are adding an existing key that has a different name, replace id_rsa in the command with the name of your private key file.
```
ssh-add -K ~/.ssh/id_rsa
```