It declares a function called myFunc which returns an int and takes two int parameters. This function has to also be a virtual member function of some class, because the =0 part at the end is the "pure-specifier" which means that the function does not have a definition (implementation) which is only allowed for virtual member functions, making them pure virtual functions. With pure virtual functions, you force the derived classes to provide an implementation for them, also making the base-class an abstract class, meaning that only derived class objects can be created. Abstract classes are sort of the C++ flavor of what is traditionally called "Interfaces" in the Java/C# OOP terminology.
For Each ctrl As Control In Me.Controls("pnlMainPanel").Controls
If ctrl.GetType Is GetType(System.Windows.Forms.Panel) Then
For Each subCtrl As Control In ctrl.Controls
If subCtrl.GetType Is GetType(System.Windows.Forms.TextBox) Then
If subCtrl.GetType Is ...