1. Download and install it. Then put in your server IP:Port in the program once you launch it. It'll show you (right away) the status of the server you put in. The players connected, latency to the server, etc. All public information from querying the server. You can then put your RCON password into the RCON tab, and then click the 'Get Log (Internet)' button to start streaming your server's console log to HLSW. This lets you see pretty much anything you'd normally see on your game console right in HLSW in the Console tab. You can also run console commands. It also let's you view and send chat messages to the server. You NEED to input the RCON password for console/chat features to work.
2. ^ Answered this is question #1. It's essentially a remote console program. Very VERY useful for server owners. Especially if you run more than 1 server as you can have as many servers in your server list with HLSW as you want and toggle through them.
3. No. You'll still need FTP or Remote Desktop to do this.
4. Yes it's 100% free. You don't need an account to use it either. When it asks you to log in when you launch the program, just click offline. The login thing is just a buddy list/friends thing they tried implementing which isn't supported anymore anyway.
If you have any other questions, feel free to ask. I've been using HLSW for years. I love it!