purchasing books or podcasts from Apple

Would someone be able to explain to me, in English, how to do the following?

From my Mac, clicking on the icon that is a red circle with a white musical note, or clef, inside it, and entering what I believe is known as an "iTunes store".

Selecting a podcast or a book, and transfer it to my Mac.

Transfering it from my Mac to a 2010 vintage iPad, so that I can listen to it while walking, since it would be ridiculous to carry around my Mac to listen to it.

Please baby-step me through this, as words like upload, download, iMac, apps, iStore, streaming, et.al. are not in my English dictionary and I don't know what they mean.

Thank you! David