Taking Information From One Window And Putting Into Another

I am developing a game and I want an options window to be used so that the user enters data into this and it carries to the main window instead of being lost. I tried it with my recent program , guess the color , but it did not work the way I thought. I thought that I could assign it to a string in a textbox to a variable and it would carry into the main window...

I want this to happen:
The user begins the program by clicking shortcut
User clicks options in the toolbar
A new window comes onto the screen

In this window the user will select a map size then click ok the verify , radiobuttons used in this example...
Back to the main screen after clicking ok
User clicks new on toolbar to begin game
Game is then playing...

Form1 <<< Form 2
game screen 3x3 button
end turn

Form 1
New game is begun
form 2 appears
3x3 button is pressed*
variable is used to change map (there is only one map for now)*
form2 closes and form1 shows
End turn is clicked