Threading in C#: .join obligotory?

so i am just learning about Threads in C# and a question arose.

I have a TCP-Server-Class wich accepts connections and passes them to a TCP-Client-Class.
The code roughly looks like this:
(dummy Code)

Class TcpServer
{
    public static Main(string[] args)
    {
       while(true)
       {    
          //I create a new instance of my "TCP-Client-Class" and pass the accepted connection to the konstruktor
          ConnectionHandler client = new ConnectionHandler(TCPListner.acceptconnections);

          //create a new Thread to handle that connection
          Thread client1 = new Thread (client.handleConnection()); //and start handling it
          client.start;

          //Do some other stuff for protokolling
          do.someOtherStuff;
       // and then wait for a new connection
       }
    }    
    //Some other Methods ect.
}

Class ConnectionHandler
{
   //Konstruktor in wich a connection TCPclient connection has to be passed
   public ConnectionHandler(TCPclient client)
   {
      //Do stuff
   }

   //Method to handle connection
   public void handleConnections()
   {
      //Open streams
      //.
      //.
      //.
      //close streams
      //close connections
    }
}

Now to my questions:
a) Is it obligotory to close that Thread again, after it reached the "close connection" part?
b) To close a thread do i just have to call the .join Method in my main class or is there anything else i have to take care about.
c) Incase of an error, can i just simply leave the "handleConnection()" method and close that thread (ofc with apropriate error-handling)?
d) Is it important to drop the "client" reference or the "client1" reference? Or is it just consumed by the garbage collector?