How To plus And Show Value ?

It's better you can create a new button like Calculate and in the button click event you can get all the text value and add it and bind to the total textbox. Otherwise you can create the textbox click event and in that add and display it. See this link for example of click event, https://docs.microsoft.com/en-us/dotnet/api/system.windows.forms.textboxbase.click?view=net-5.0