As flatthumbs88 says below, 'das Buch' changes to 'die Bücher' in plural form (as all German plurals are 'die'), and that also affects other words including ihr, which becomes ihre.
The sound made by ü doesn't exist in English: it is done by pronouncing a 'ee' sound but with your lips rounded as if you were saying a 'oo' sound.
There is no direct equivalent of the sound of 'ch' here in English, though it is very close to the way h is pronounced in the word 'hue'.
The -er ending is pronounced like a short 'ah' sound: the r is hardly pronounced, if at all.
You can listen to the pronounciation of Bücher (and other German words), on forvo: https://forvo.com/word/b%C3%BCcher/#de
I am confused as to why it is 'Ihre' and not 'Ihr'. Buch is neuter so doesn't this work out then as ihr?
Never mind, I think I just figured out the answer to my own question. As the noun involved is plural, which is 'die', that's why it translates as ihre.
If I am wrong, feel free to tell me!
Sounds like a solid logic to me, and Google Translate agrees, but I am just teaching myself too, so I can't certify.
Why not seine Bücher? When have we to use sein, and when ihr? This confuses me.