You can add SSH key to the ssh-agent on different platforms discussed further.

Linux

Use the following command on Linux system to add SSH key

cat /home/<local-user>/.ssh/id_rsa.pub

Windows

Open the GIT GUI and go to Help → Show SSH Key as shown in the following image.

Then, click the Copy To Clipboard button, to copy the key to the clipboard.

Mac

In Mac OS X, you can copy id_rsa.pub contents to the clipboard using the following command.

$ pbcopy < ~/.ssh/id_rsa.pub