1 Unos when you try to say something in plural and is in masculine like Unos Perros (some dogs) is like some but in masculine.
2 Unas when you try to say something in plural and is femenine like Unas motos (some Motorcycles) Motorcycle in spanish is moto and is in femenine for know when write the words "unos" and "unas" you need to know first what gender is the word that you will use.
3 Un is use when you try to say something singular and masculine like Un celular (a cellphone) and again "Un" for masculine words and "Una" for femenines words the only change is that now is not in plural now are in singular.
