Hey no problem we all have to learn.  Basically an interface is just that just a set of properties and methods that tell you how to access a class.  So they naturally come with no code.  However when you impliment an interface you also have to impliment the code to define that interface.  For example: 

using System;


namespace Dados
{
    public class Manutencao : IDados
    {
        private string _nome;
        private string _idade;


        public Manutencao() { }


        public string Nome
        {
            get { return _nome; }
            set { _nome = value; }
        }


        public string Idade
        {
            get { return _idade; }
            set { _idade = value; }
        }
    }
}