Easy: you just need to change one line:
textfilestream.WriteLine(Product & " " & Size & " " & Cost)
becomes:
textfilestream.WriteLine("Product: " & Product & " Size: " & Size & " Cost: " & Cost)
Or there is the advanced version:
extfilestream.WriteLine("Product: {0} Size: {1} Cost : {2}", Product, Size, Cost)
This make look complicated, but all it is saying is "Where I have a pair of curly brackets, replace this with a value from the list at the end". So "{0}" is replaced with the first parameter, "{1}" by the second and so on. Later, you will learn how to use this to change how numbers and so on are displayed. It's simple when you get used to it!
[edit]Format string version add - OriginalGriff[/edit]
"Well I have a combobox with 3 items namely: Product Size and Cost.
I have also a maskedtextbox.
If I select "Product" and "Size" on the combobox, I want to disable the maskedtextbox from filling, how must I do it?"
That's more complicated, and I'm not sure you have enough background for it yet.
So if this is gobble-de-gook to you, I'm not explaining it! It can wait until you reach it in your course.
1) Handle the SelectionChanged event for the ComboBox.
2) In the handler, if the selection is "Product and Size" then set the MaskedTextBox.Enabled property to false.
3) Otherwise, set it to true.
You will probably need to set the property correctly in your Form.Load event as weell to ensure it is OK before teh user clicks anything.