"Apfelsaft trinke ich"?
"Apple juice drinks I"? Is there some cases in German where the word order is switched?
It can be switched for emphasis. With some exceptions (notably, questions), the main verb always comes second in German, so you can say "Ich trinke Apfelsaft heute" (default), or "Heute trinke ich Apfelsaft" (to emphasise the "today"), or "Apfelsaft trinke ich heute" (to emphasise the applejuice). That said, this is an... unusual word order. The closer analogue in English would be "[It is] Apple juice I'm drinking" (as opposed to the orange juice that everyone else has), and as with that sentence in English you have to kind of set up a situation for it to make sense.
German has a much more flexible word order than English, because they use inflections and declensions to show which is the subject and which is the object or indirect object of a sentence.
In English we must say:
'The dog bit the man' because 'The man bit the dog' has a completely different meaning, but in German, you could either say 'Der Hund beisst den Mann' or if you want to emphasise that the man was bitten you can say 'Den Mann beisst Der Hund' the 'den' shows that 'Mann' is in the accusative case and is the object of the sentence so the meaning is still clear despite the word order being different.
blahedo is not exactly right. Normally "Apfelsaft trinke ich heute" puts emphasis on the subject ("ich"), whereas "Ich trinke heute Apfelsaft" puts emphasis on the Object ("Apfelsaft"), and "Heute trinke ich Apfelsaft" puts emphasis on the time ("heute"). Furthermore "Apfelsaft trinke heute ich" is possible. Beware: Neither "Ich trinke Apfelsaft heute" nor "Heute ich trinke Apfelsaft" (representing the common phrase composition in english) are valid sentences in German!
As far as I know, you're free to swap the order around. Hence "Apfelsaft trinke ich" and "Ich trinke Apfelsaft" mean pretty much the same thing.
The conjugation of the verb helps you to tell that it's I that's doing the drinking (because it's "trinke" rather than "trinkt").
It is worth adding that the place of the verb is fixed for every kind of sentence. In normal cases in present tense the verb is in the 2nd position (which is different from the 2nd word), as in: Der Hund beisst den Man. In some past tenses it is in the end, as in: Der Hund hatte den Mann gebissen (the dog had bitten the man). The verb also moves to the end in yes or no question and other cases, but it is impossible to get into all of them. The point is it is not up to the discretion of the speaker.
If I'm understanding, that form of expression is to emphasise the object. That's used, as an example, when you go to a bar. The waiter ask you and your friends what are you gonna drink: your friends say "we're gonna drink beer", an then you say "apple juice drinks I", not milk, not water, not beer... I want to drink APPLE JUICE
To address kawiah's stance: Nononono!
Flexible word order has absolutely nothing to do with active/passive distinction.
The correct German sentence, if expressed in the passive form, would be:
"Der Mann wird vom Hund gebissen" (The man was bitten by the dog).
"Vom Hund wird der Mann gebissen" would also be grammatically correct, but rather unusual.
Note that, like in the active form, the personally, temporally conjugated verb (in this case the auxiliary verb "werden" (- "er wird [gebissen]") is in the second position in the sentence, no matter whether the sentence starts with the subject or the object.
As people stated before, the verb HAS to be the second word in a sentence. The other words can be placed according to the way you want them emphasised. This goes for simple sentences (where the verb is in active form), for example: "Ich ESSE Spaghetti "( I eat spaghetti) In case you have to use passive forms or some past tenses, where the verb complex is composed by an active verb and an infinitive form, for example: "Ich HABE Spaghetti gegessen" (I have eaten spaghetti) "Spaghetti WIRD von mir gegessen" (spaghetti is eaten by me) the "real" verb (active form verb) goes in the second place, while the infinitive form is placed at the end of the sentence. Hope this helped :)
Regardless, the verb always comes in 2nd position in a sentence (except in other types of sentences, i.e. with "dass"). Pretty much everything else can be switched around for emphasis or style purposes. It is though, a weird choice to put this kind of word order in the beginners' lessons.