How do I Read/Write variables to and from a file?

Question

 How do I Read/Write variables to and from a file?

I want to be able to read the variables for my C# Console app from a file and everytime there is a change I want the program to write the changes into the file also.

I have the following setup at the beginning of the program's Main.

 

var usermainmenuselection = "";
var user_settings_allowbeep = true;
var user_settings_textiscolor = false;
var optionsselection = "";