Check out example codes for "c# serial port". It will help you in understanding the concepts better.

Code Example 1

//Serial Ports are used to communicate with other independant devices over 
//a serial COM. More at and
//For windows .NET Framework (This will not work in .net core or on linux)
//You will be using IO.Ports
using System.IO.Ports;

//Only one source can use a serial port at a time so encaposlation is important
class MySerialPortClass : IDisposable
  	//This is the class that will do most of the heavy lifting
	public SerialPort SerialPort { get; private set; }

	//diffenent devices use diffent baud rates or rates of electrical symbol 
  	//change. This will cause diffent rates of communication, but both devices 
	//must agree on a rate to exchange at. The most common is 6800 bauds.
  	const int DefualtBaudRate = 6800;
  	//The above is also true of the amount of bits in a attomic ecnoding in a 
  	//message.The most common is 8 bits for a byte. Honesly this one rarely changes.
  	const int DefaultSize = 8;
  	//The same is true of the party bit. The party bit is to detect error.
	//Hardware is often good enough now that is is not used often, but it adds
	//a bit to the start and sets it to make sure the number of set bits is odd
	//or even. Or it can be used to just mark the start, but stop bits are 
  	//enough usally to mark at the end.
  	const Parity DefaultParityBit = Parity.None;
	//Stop bits or period is to mark the end of a message. Usally one bit is used.
	const StopBits DefaultStopBits= StopBits.One;
  	//since only one source can access a com at a time you may want to expose 
  	//if it is open. It will also be useful for resource freeing after.
  	public bool Open { get; private set; } = false;
  	//It will also be useful for resource freeing after.
	private bool Disposed { get; private set; } = false;
  	//In Constructor we should set all the com vars. But the one we havent
    //defined a default yet is the com port name. This will change depeneding
   	//on the plug used or if a virual (USB) on is used. Check your 
  	//'Device Manager' for valid ports it could be. 
  	MySerialPortClass(string ComPort, int BaudRateValue = DefualtBaudRate, Parity Par = DefaultParityBit, int DataSize = DefaultSize, StopBits Stop = DefaultStopBits)
  		SerialPort = new SerialPort(ComPort, BaudRateValue, Par, DataSize, Stop);
	//after all the set up you must open the port. If the port is in use you
	//will get an exception and you may need to rest it or your computer to
  	//get it open. Agan only one source can use a port at a time.
	void OpenPort()
    	Open = true;

	//reading and writeing is simple after set up and opening, but for each 
	//device messages will have to be formated differntly. Check with your
	//devices manual or data sheets for more on formatting. 
  	//can read a single byte at a time for decoding messages as they come in
	byte Readbyte()
      	return (byte)SerialPort.ReadByte();//cast is because dispite it being a byte ms made it an int container
  	char ReadChar()
      	return (char)SerialPort.ReadByte();//cast is because dispite it being a byte ms made it an int container
  	//or you can read a string out if you know messages are on a line or 
  	//would rather mass decode
  	//to read all in the buffer into a string
  	string ReadExisting()
      	return SerialPort.ReadExisting();
  	//if you know messages are a line like in a doc
  	string ReadExisting()
      	return SerialPort.ReadLine();
  	//Lastly you can decode as a buffer if you know message lengths
  	//Not it will fill in the buffer you provide and not size.
  	public int Read(byte[] buffer, int offset, int count);
      	return SerialPort.Read(buffer, offset, count);
	//You can simply write a sting out
  	public void Write(string text)
      	return SerialPort.Write(text);
  	//Or you can write from a buffer like in a stream
  	public int Write(byte[] buffer, int offset, int count);
      	return SerialPort.Write(buffer, offset, count);
	//Or you can write a line from a string
	public void WriteLine(string text)
      	return SerialPort.WriteLine(text);
  	//Lastly it is recomended thay you dispose of your class and free system
    //Close will free the port for use by a different source
    void Close()
    	Open = false;
    	return SerialPort.Close();
    //allows a using statement to dispose after use elegantly
	public void Dispose()
    	Disposed = true;
    //in the garbage collection ensure disposal so port will open back up after.


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