What is the American accent?

American accent is a combination of three main components: intonation, liaisons, and pronunciation.

Intonation, or speech music, is the sound that you hear when you hear a conversation, but you can not understand what it is all about, because you can’t identify meaning of words and phrases, but you can tell the nationality of the speakers, because every single nationality have their own unique intonation.

The American intonation dictates liaisons and pronunciation. By liaisons I mean word connections or sound units (how these words are come together in the form of phrases or how they are connected to the sound units). Americans do not speak word by word. The individual words are connected to the sound units.
Pronunciation is the spoken sounds of vowels and consonants and different combinations. Pronunciation is not so big deal. If your intonation is close to the intonation of the native speakers, they usually can understand you even if your pronunciation is far from excellent.