The online review can simply amount to choosing a star, or a simple comment such as Joe was a fine character who reminded me of my crazy uncle. Or you can write hundred of words and consider submitting to the New York Times and maybe discovering a whole new career.
Regarding the post, here’s where to go:
On Apple Books, click in the menu on Ratings and Reviews
On Amazon, scroll way down the page and keep and eye on the left side.
At Barnes and Noble (alias Nook) travel straight down the page to the Customer Review section.
At Kobo (or Rakuten Kobo), scroll straight down to the Ratings and Book Reviews section.
At Scribd (my favorite as you can subscribe for $9.99 monthly and get all the ebooks and audiobooks you care to consume) head straight down the page to the Reviews section.
On Smashwords, you need to purchase the book before you can review it. Once you buy it, even using a free coupon, go to the right side menu and click Leave a Review, which will deliver you to the review section.