What line of code does get the information?
Well, the key is in the two lines that you have in LoadServer_Click. First, you call Activator.GetObject to create an instance of the method in the remote server. And then you do ds=dss.GetDataSet(), which execute on said instance the method that obtains the data.
This will work, but as someone already commented it is considered obsolete nowadays. If you are looking at this for some new software that you are going to develop (as opposed to learning how it works for the purpose of maintaining a legacy application) then you should consider other more modern options, such as a REST service or at the very least WCF, but not .Net Remoting.