Can anybody teach me all i need to know about the word "IS".?

Question

Cuz sometimes i hear people saying IS at the end of their sentence (LIKE: I dont know what it is), and sometimes i hear other people say IS in the middle of their sentence (LIKE: I dont really know what is the price of this). Can anybody please help me, i really need some help. One other thing, i just made this up but im not sure if its correct or not (I dont really know what the cost of this is). What would be more appropiate, my made up sentence or the sentence before my sentence (the second one)?

Answer 1

"is" is the present tense form of the verb "to be"

"To be" verbs are all the various forms of that verb: am, is, are, was, were, has or have been, had been, will have been, being, and to be.  They are used to link a subject with a noun or adjective.

A verb of course, is a 'doing' word.  

Answer 2

the one with "is" at the end sounds better and more naturali dont think "i dont really know what is the price of this" is correct.