The article is just wrong. There's no such thing as static/dynamic arrays in .NET. Arrays in .NET are fixed length. I will point out that what figuerres said about List is a bit misleading... you can use LINQ on Array types just as easily as you can on List types. Other than that, he's correct. The List type is what you'll want to use, in general, for a collection type that can change in size.
All that said, you can "declare an array without knowing its size first." Array declarations don't specify a size.
int a; // No size specified
This array reference can now be assigned to any integer array of any size.