send and receive command from serial port to textbox in c#

Question

Hi

   I am doing one project using serialport. I have three forms in one form i receive command 'g' from serial port and display it to text box based on specify time interval. And in another form i want to receive command 'c' from serial port and display it to textbox and also wand to send data from textbox to serialport to update that value through one button click. And in last form i want to receive command 'v' from serialport and display it to textbox and send the data  from textbox to serialport through button click. I have no idea to start this code... Please help me....  i am new in using serial port communication....

Thanks in advace