A response file contains your answers to specific questions asked by an interactive package. An interactive package includes a request script that asks you questions prior to package installation, such as whether or not optional pieces of the package should be installed.
If you know that the package you want to install is an interactive package, prior to installation, and you want to store your answers to prevent user interaction during future installations of this package, you can use the pkgask command to save your response. See pkgask(1M) for more information on this command.
Once you have stored your responses to the questions asked by the request script, you can use the pkgadd -r command to install the package without user interaction.