1. Copy your files to ~/.ssh.
cp /path/to/my/key/id_rsa ~/.ssh/id_rsa
cp /path/to/my/key/id_rsa.pub ~/.ssh/id_rsa.pub
  1. Change permissions of files
sudo chmod 600 ~/.ssh/id_rsa
sudo chmod 644 ~/.ssh/id_rsa.pub
  1. Start the ssh-agent in the background and add the key to agent
eval $(ssh-agent -s)
ssh-add ~/.ssh/id_rsa

NOTE: If using fish shell,then just execute the ssh-agent -s and then export those printed vars. No need to import public key.