Choose JNLP or SSH to launch your agent.
JNLP
Make sure container can access Jenkins master. Take image jenkins/inbound-agent as a reference
SSH
Make sure container initialize with a SSH server. Take image jenkins/ssh-agent as a reference
If using SSH, here is a sample of arguments:
Docker image: jenkins/ssh-agent
Command: setup-sshd
Environment Variable: Key: JENKINS_AGENT_SSH_PUBKEY, Value: Your public key
Launch Method: SSH