Declaration method in users Class

What's different between declaration method in these codes

class Programm
{
     ClassA class1 = new ClassA();
     class1.TestMethod();
}


public ClassA
{
     public void TestMethod()
     {
     }

}

and

class Programm
{
     ClassA.TestMethod();
}

public ClassA
{
     internal static void TestMethod()
     {
     }

}