<OutputPath>bin\Debug\</OutputPath> for debug and
Right click on project -> Properties -> Signing tab -> Check "sign the assembly" -> Navigate to the location of the key
If your plugin was successfully deployed to Packages folder put the breakpoints in you plugin and open Studio. Because the plugin is a class library we need to attach to Studio process in order to debug.
In Visual Studio go to Debug tab-> Attach to process
In the process list search for SDLTradosStudio.exe and attach to process