Yeah, when i first saw the letters and accents i got pretty scared. But i must admit, took me like an hour for me to learn the alphabet, and totally worth it. Now i can read a word in Polish (even without knowing what it means). This is very helpful, i totally recommend doing the same. :)
Ehm... no, you NEVER say neither "Jestem jem jabłko" nor "Jestem je jabłko". They make no sense. The first one means "I am I eat an apple" and the second "I am he eats an apple".
Don't try translating "to be" in the Present Continuous construction. "I am eating" is just one verb, not two.
"je jabłko" is "[he/she/it] is eating an apple".
"Jem jabłko." is indeed "I am eating an apple."