Hay (sounds like the English eye) means there is or there are.
So Hay is actually one word for the there is or there are in English.
So you can form sentences with this word without need to worry about the grammar of verbs.
Hay + vocabularies you learnt will give you many ways to express yourself. It is usually used to express that something can be found in some place. Put it in question form will allow also to ask about things you need to find particularly is you are a tourist.
The nice thing also is that the question sentence is the same in structure like in regular sentence you just needed to end with a question mark and you need to express it like you are asking a question. Thus Hay is considered as a question word.
Hay un libro en la ban(y)o?
Si, hay un libro en la ban(y)o.
Hay is followed by indefinite article as un, una or other numbers (tres, quatro---). if to follow a pleural form the article is omitted. Spanish definite articles never follow Hay.
No is used before Hay to make the sentence negative:
No Hay libro en la Ban(y)o.
