SQL Joins in C#

Question

I am working on a project that is supposed to communicate with an SQL Server 2012 database. Currently, I've got a dataset of all the tables in the database, and I am trying to come up with a way to perform a complex query with several joins in this application.

 

Thus far, I can create a dataset with the information from 1 of my tables, but I cannot join or do subqueries or otherwise change the data received. How do I utilize my dataset so I can create joins of data from several tables? This is my first time interacting with an online database with a C# program, so I'm a little lost as to how to make this work. Any help anyone can give will be appreciated.