I'm a bit confused. Shouldn't it be in Instrumental case after "To jest..."?
Nominative is used as a complement of the identifying phrase to jest/są - that is/those are: To jest nowe muzeum. That is a new museum-Nom. To są moje okulary. Those are my eyeglasses.
The pronunciation is a bit tricky for me here. It sounds as though the "ks" at the start of the word "książka" is pronounced like the English "ch". Is that correct?
You mean "ch" as in, for example, "each"? No, that's the 'cz' sound.
The first two sounds of this word are "k" and "si" (=ś, palatalized s). I rather wouldn't think of them as a compound.
I really dont know about rules in polish since i dont know anything about polish but whats the differece between książkę and książka? Is the gender or something???
Książkę is the accusative (direct object) form of książka. So when the book is doing something (sitting on the table, say), then it's książka. When someone's doing something to the book (like, I don't know, reading it maybe), it's książkę.