What it means
A CTA includes both the invitation and the surrounding context that makes it meaningful. It may be a button, a link or a short section. Its effectiveness depends on whether the destination and commitment are clear, not simply on making the button brighter.
Use it in practice
Use a label that describes the action and place it where the visitor has enough information to decide. Give the main action a clear visual priority.
Watch out for
Several equally prominent actions can compete. Avoid vague labels when a specific verb would explain what happens next.