I've used a downloader plugin quite a long time ago with phonegap 2.2 and it was quite easy to use.
Is this the plugin you are trying to use? or maybe this one?
The fist one seems to have been updated for the phonegap 2.7+ format so maybe usable in a phonegap 3 project, except that you won't be able to install using the CLI and will have to had the plugin manually in platform/android or you could write a plugin.xml yourself.
To use it, you just have to follow the instructions in the readme.md or read the original article in http://www.toforge.com/2011/02/phonegap-android-plugin-for-download-files-from-url-on-sd-card/
Again I haven't tried to use it in recent versions of phonegap and am not sure if the plugin should be updated to be compatible.
Edit:
For each file you have to call:
window.plugins.downloader.downloadFile("http://server/file.txt", {overwrite: true},
function(res) {
//function called when the file is downloaded
//the file content is in res
}, function(error) {
//function called in case of error
}
);
if you need to download several files, you could download the next file in the function called in case of success.