So here is how to do it with application settings:
1) Add a TextBox to your form
2) In the Properties window, expand down ApplicationSettings
3) Click in the area of (PropertyBinding) to get the ellipses (3 dots), then click on that to open a dialog window
4) In that dialog window, scroll down to the Text property
5) Click the drop-down for Text and select New, then another dialog window will pop up
6) In the Name property of that dialog window, put any name you wish to call it (referred to as the setting name)
7) Click OK to the 2 dialog windows
Run the application
9) Type something in the TextBox
10) Close the application
11) Run the application again
12) You should see the value you put in the TextBox still there