Why is sometimes 'et eple' or 'eplet'? I don't understand it and don't see any differens.
'Et eple' means 'an apple', 'eplet' means 'the apple'.
What is the difference between en and et?
The indefinite article changes depending on the gender of the noun. We use "en" for masculine nouns, "et" for neuter nouns, and "ei" for feminine nouns.
"En" for feminine nouns works as well. But not vice versa.
Your vice versa is vague