sentence structure, order
So far I have learned about the accusative and nominative cases in the second set of basic lessons.
Does sentence structure matter as long as the nominative and accusative cases are clearly defined?
"Das Mädchen hat den Apfel"
"Den Apfel hat das Mädchen.
Both structures are correct. More complex sentences can have several different possible structures. The structure to choose depends on what you want to emphasise. For example:
There be a family and an apple.
- > "Das Mädchen hat den Apfel, aber der Junge hat ihn nicht."
There be a bowl of fruit, a boy and a girl.
-> "Den Apfel hat das Mädchen, aber die Birne hat der Junge."
Also, don't forget that the accusative case only changes the masculine article. It can get confusing if you try using the alternate sentence structure with only feminine or neutral nouns.