If you don't have ssh key, open terminal and run following commands:
cd ~/.ssh
^
ssh-keygen -t rsa -C "your_email@example.com"
When you have ssh key, just copy public part to clipboard:
xclip -sel clip < ~/.ssh/id_rsa.pub
To install xclip run:
sudo apt-get install xclip
Then add to GitHub or GitLab keys in profile settings