On github you need search by Settings.

Settings

Then, in the next page, search for SSH and GPG keys

SSH and GPG keys

In the next page click in New SSH Key

New SSH Key

Now, in your terminal:

ssh-keygen

For the messages below only press enter

Enter file in which to save the key (/home/vagrant/.ssh/id_rsa):

Enter passphrase (empty for no passphrase):

Enter same passphrase again:

At this point your keys (private and public were generated)

cat ~/.ssh/id_rsa.pub

copy the content and paste in the github

ssh key

Just click in Add SSH Key and your ssh is available for use it.