I have C&P how to borrow /lend below.
Amazon's Page on Lending Kindle Books (including how to figure out if a book is Lendable, how to lend and how to receive a loaned book). LOTS OF USEFUL SCREENSHOTS: amzn.to/gS9lbx
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Is My Book Lendable?
Titles that are eligible for lending, as determined by the publisher or rights holder, will have a message on the product detail page. Scroll down to the "Product Details" section and look for "Lending: Enabled" (under the ASIN number - you will not see anything about Lending if the book is not Lendable).
If you already own the book, you can also see if it is Lendable by checking the Your Orders section in Manage Your Kindle. Click the "+" symbol next to a title to reveal additional information about the title. If lending is enabled, you'll see a "Loan this book button" next to the product image.
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Loaning a Kindle Book
If you own a book, you can lend it from the Manage Your Kindle page or from the book's Product Detail Page on Amazon.com. You'll enter the borrower's name and e-mail address and an optional notification message. Your recipient can receive the book loan even if they do not yet have a Kindle or Kindle reading application.
From Manage Your Kindle: Manage Your Kindle lists all of your Kindle content purchases under the Your Orders section. Click the "+" symbol next to a title to reveal all information and options. If lending is enabled, you'll see a Loan this book button next to the product image. Click the Loan this book button. You'll be directed to a form where you'll provide the borrower's name, e-mail address and an optional message. THERE ARE LOTS OF HELPFUL SCREENSHOTS OF THIS PROCESS AT AMAZON - CLICK THE LINK AT THE TOP OF THIS NOTE.
From the Product Detail Page of a book you have ALREADY purchased: When logged in to your Amazon account and looking at the product detail page of a book you have already purchased, a notification at the TOP OF THE PAGE will indicate that you already own the title. If lending for the book is enabled, you'll see a second notice: "Loan this book to anyone you choose." Click the Loan this book link. You'll be directed to a form where you'll provide the borrower's name, e-mail address and an optional message. Your loan recipient will be notified of the loan through the e-mail address you provide. SEE THE LINK AT THE TOP FOR AMAZON'S PAGE WITH HELPFUL SCREENSHOTS.
More About Loaning: The borrower has seven days to accept the loan. If the loan is not accepted after seven days, the book will become available again through your Archived Items. You can also attempt to loan the book again at that time. If the borrower already owns the title, or the title is not available in the borrower's country due to copyright restrictions, the borrower will not be able to accept the loan. In these cases the lender will be able to read and loan the book again after the seven day period has ended.
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Receiving a Kindle Book Loan
If someone has loaned you a Kindle book, you will receive an e-mail notification allowing you to download the book to your Kindle device or free Kindle reading application. After accepting the loan, you'll have 14 days to enjoy the book until the download ends.
To download a Kindle book loan: Open the e-mail message you received about your book loan and click the Get your loaned book now button. Your web browser will launch and automatically direct you to Amazon.com to accept the loan. Log into your Amazon.com account if prompted, or create one if you are not yet an Amazon.com customer. You may also be prompted to enter a billing address to verify your location only (there is no charge associated with accepting a Kindle book loan.) If you are already a Kindle user, just select the device that you would like the book delivered to from the drop-down menu and click the Accept button. If you do not yet have a Kindle or Kindle reading application, click the Accept button and you will be taken through the steps to download a free reading application. After downloading a reading application you will need to return to the e-mail message and accept the loan. Tip: You have seven days from when you first received your e-mail about the book load to accept the loan. Once you accept, you have 14 days before the loan expires.