"The eyes see an apple."
Translation:Die Augen sehen einen Apfel.
I'm not sure what your question is or what the issue is, but I'll try to clarify things....
"Die Augen sehen ein Äpfel" is wrong for two reasons:
1) Äpfel is the plural of Apfel. So you cannot have "an apples".
2) The case is accusative, so it is "einen" not "ein".
Additionally, "a apple" is wrong in English. It is "an apple".
More info on cases here: http://coerll.utexas.edu/gg/gr/cas_01.html
Hope that helps!