ElefantPhace provided an answer for Music.

Here's for Books:

You can access your books on different devices, including compatible Android devices, iPads, iPhones and iPod touches, or on the web on your computer. No matter where you read your books, when you're connected to a network (via Wi-Fi or a data connection on your device) we'll automatically keep track of your reading place, so you can pick up right where you were last reading the next time you open your ebooks

Note: In rare occasions when a user tries to access books on a number of devices at the same time, our system may temporarily block them from opening new reading sessions. This can happen when too many readers are open on different machines or browsers. If your other reading sessions are closed or inactive, you will be able to read in this browser after a short delay. If you believe this is an error please contact our support team.

ElefantPhace provided an answer for Music.

Here's for Books:

You can access your books on different devices, including compatible Android devices, iPads, iPhones and iPod touches, or on the web on your computer. No matter where you read your books, when you're connected to a network (via Wi-Fi or a data connection on your device) we'll automatically keep track of your reading place, so you can pick up right where you were last reading the next time you open your ebooks

Note: In rare occasions when a user tries to access books on a number of devices at the same time, our system may temporarily block them from opening new reading sessions. This can happen when too many readers are open on different machines or browsers. If your other reading sessions are closed or inactive, you will be able to read in this browser after a short delay. If you believe this is an error please contact our support team.