When the statement is an adjective, 'van' is omitted in the present tense unless the sentence has an imperative or a conditional mood. When the statement is an adverb, 'van' is always present in the sentence.
- A busz kék. = "The bus is blue."
- A busz gyors. = "The bus is fast."
- A busz a buszmegállóban van/áll. = "The bus is in the bus stop."
- A busz két autó között van. = "The bus is between two cars."
Also, when the statement is a noun, 'van' is omitted:
- A busz egy jármű. = "The bus is a vehicle."
- A busz nem játék. = "The bus is not a toy." or "The bus is no toy."
The word before the verb "van" is emphasized. So in the sentence: "A busz kint van", the emphasis is on "kint" (i.e. outside). And in the sentence "A busz van kint", the emphasis is on the "busz". However, this second sentence depends on the reference to the other vehicle.
Yes, "van" means is. For the second part you may want to check out http://www.hungarianreference.com/Van-is-exists-omitting.aspx