Difference between template and mixin template

[Just Dave]

I'm trying to get my head around mixing templates. I'm using it 
as kind of a replacement for class inheritance as it seems to fit 
better composition over inheritance. So I do something like:

     mixin template NumberTemplate()
     {
     private:
         int number = 0;
     public:
         int getNumber(int number)
         {
             return number;
         }
     }

     interface INumber
     {
         getNumber(int number);
     }

     class Number : INumber
     {
         template NumberTemplate;
     };

So two questions:

a) Is this correct usage?

b) It compiles if I just do:

     template NumberTemplate()
     {
     private:
         int number = 0;
     public:
         int getNumber(int number)
         {
             return number;
         }
     }

what is the difference between template and mixin template?