The most comprehensive site for this specific workbook is OnlineGDZ.3dn.ru , which provides a step-by-step breakdown by Einheit (Unit) and exercise number.
Онлайн ГДЗ. Ответы к "Горизонты" рабочая тетрадь 5 класс gdz po nemetskomu iazyku 5 klass averin tetrad
For targeted help with a single difficult page (like translations or complex syntax), you can often find documents on sites like Scribd that provide full translations and completed tables. The most comprehensive site for this specific workbook