Quote Originally Posted by луна
When one says "на завтрак я беру сок" сок is accusative. Is it an accusative because it 's a direct object?

It is the same when one says "на обед я готовлю салат"? Is it also a direct object?
Exactly the opposite. An object is classified as direct because—and if—it is in accusative, not the other way around. And object in dative, for example, is regarded as indirect in Russian, even if it follows the verb without any prepositions.

Quote Originally Posted by луна
and when you use "ложиться спать" is this a movement? So does one have to use the accusative case?
"Спать" is not a noun, it is a verb (to sleep), so you can't talk about cases here.

and the verb любить, is it always followed by an accusative?
Yes and no. If it has an object, it is in accusative. But you can just say "Я люблю" (I am in love), and the verb won't be followed by anything.