Backend Supported Unity Game - ASP.NET

Hi Guys,

I would like to know what is the best practice for Unity games to communicate with server, especially ASP.NET backend supported server?

Example:

1) Getting HighScore board & Storing user score into Database

2) Checking user session

3) Real Time chat-room among online players.

4) Best JSON serialization/de-serialization library/code file/dll (free) available for Mono development.

I do hope you guys will not getting frustrated to explain to me because I'm totally newbie to this powerful game dev tool. Cheers~ :)

Thanks!