When you write a post, Blogger automatically generates a permalink based on the title of the post. Until now, blog authors have had no control of the permalink. Custom permalinks give you more control of your blog and posts. These new custom links also provide readers with more information about your post when scanning search results.
If you prefer to use a custom permalink, you can do so via the “Permalink” option in the Post Settings box.
To create your own URL for a specific post, simply select “Custom URL”, and enter your new URL in the field below. If you wrote the post in June of 2012, your new URL will look like this:
The bolded area is the portion of the URL that is customizable.
If the custom permalink you entered already exists, Blogger will attempt find a free one for you.
At present, the characters allowed in a custom URL are limited to: a-z, A-Z, 0-1. The only special characters available are underscore, dash, and period.
Click here to read more about custom permalinks in the Blogger Help Center.