Creating a simple class in C# to gather data from SQL

I'm trying to learn proper way of defining classes. I have two classes where Person is definition for every possible information about person, while Client is using information from Person and is highely connected with Person.

public class Person {
    public virtual int ID { get; set; }
    public virtual string FirmaNazwa { get; set; }
    public virtual string Imie { get; set; }
    public virtual string Nazwisko { get; set; }
    public virtual Adres Adres { get; set; }
    public virtual Adres AdresKorespondencyjny { get; set; }
    public virtual UrzadSkarbowy UrzadSkarbowy { get; set; }
    public virtual string Pesel { get; set; }
    public virtual string Nip { get; set; }
    public virtual string Regon { get; set; }
    public virtual string Krs { get; set; }
    public virtual DateTime KrsData { get; set; }
    public virtual string KrsOznaczenie { get; set; }
    public virtual string Rodzaj { get; set; } // Typ klienta (Firma / Osoba)
    public virtual string Narodowosc { get; set; }
    public virtual string ZgodaNaPrzetwarzanieDanychOsobowych { get; set; }
    public virtual string ZgodaNaPrzetwarzanieDanychOsobowychMarketing { get; set; }
    public virtual Pracownik Uzytkownik { get; set; }
    public virtual DateTime DataZmiany { get; set; } 
}
public sealed class Client {
    public int ID { get; set; }
    public Person Person { get; set; }
    public Pracownik Uzytkownik { get; set; }
    public DateTime DataZmiany { get; set; }
    public string Haslo { get; set; }
    public string Typ { get; set; }
    public void GetClient() {

    }
}

I've got 2 tables in SQL which are basically Person and Client tables with fields that are similar to those defined in c#.

Now I would like to add some methods (GetClient() and similar) to actually get Client information but since to get all Client information I need to get all Person information first. In SQL I would do query with JOIN's and I kinda get Client info connected with Person info straight away. So do I basically do it like:

    public void GetClient() {
        //SQLQUERYHERE
        Person podmiot = new Person();
        podmiot.FirmaNazwa = ...
        podmiot.Imie = ...
        Haslo = "test";
    }

Or should I do it differently?