The same dialog appears in many GSA tools. It might differ in it's design, but the functions and options are all the same.
You can add proxies here, test them and also use a scheduled function to automate this from finding new public proxies, testing and removing them again when failed too often.
The software comes with many thousand sources from where to gather new proxies and it is constantly updated. Not all providers are chosen by default and you might want to change that clicking on Add/Edit providers. In that dialog you can also add new providers or even load things from a local file.
Sorry for not finding time to describe the functions here in detail. Thats something I will have to do once I find the time.