¿Cuál es la diferencia entre det y dette ?Puedes dar oraciones como ejemplo.

Denne, dette and disse show that you are talking about something that is close to you. It's the same as "this" and "these" in English. De usually stand together with a noun, and we use denne when the noun is masculine or feminine and dette when it is neutral. In plural we use disse.
Den, det and de tell us that we are talking about something that is far from us. It is the same as "that" and "those" in English. Here too, the gender of the noun determines what form we must have. Den is masculine and feminine, det is neuter and de is plural.
The noun stands in particular form after denne/ dette / disse and den/ det / de.