1. for example Baseplayer Player, args, etc. Where can I find out when it is use and how it works?
     
  2. Decompile assembly-csharp.dll it's all in there.... Best way though is to just use Visual Studio and C# with intellisense.
     
  3. Can you should me how to find more about it using VS?
     
  4. There are already multiple threads on the subject, do a search it's all there. Basically install server on your machine w/ oxide, have visual studio 2015. Create a bogus project with references to the rust files and add your plugin file to it. When editing your plugin, you'll now have intellisence... In case of "BasePlayer player" getting passed as param, you can now do player. and the list of functions/properties will pop.

    If you want more details you can use a decompiler and decompile assembly-csharp.dll, most of the good stuff is right in there, along with definitions for most structures.
     
  5. 1) Install VS2015
    2) Download Oxide
    3) Reference all oxidemod bins
    4) Reference Assembly-CSharp from the server
    5) Compile your empty project once
    6) IntelliSense should be working now
    7) Create a post-build command with xcopy to copy the class to your server after compile.