For server access, it is mandatory to provide SSH public key. You can manage SSH keys on "SSH Keys" tab. (see Img. 1)
Click on Add SSH Key and provide name for new SSH key and optionally copy and paste your SSH public key. (Img. 2)
If public key was not provided in key create form, new SSH key pair will be generated by the system and after submitting the form, private key will be downloaded to your computer. You need to save this key in order to access the servers with it in future.