Anytime you publish a new post in blogger, Blogger automatically creates a URL address for the post using the title of the post. Usually, it uses this format by default :your blog url(e.g www.sdknaija.com)/the current year(2013)/the current month(11)/the title of the post.
For example, the title of this post is :"How to set custom Url For Blogger Posts", the URL which blogger will use for this post will be :http://www.sdknaija.com/2013/11/how-to-set-custom-url-for-blogger-posts.html.

While this might be Ok, however, there might be any reason while you like to change the post's URL, maybe for SEO purpose or for whatever reason I can't think of, it is very easy to change the post URL and set it to whichever you want. (note that you can't change the date of the post, just only the part after the date).
In a very few number of steps, you are done already.
Step 1:
Log in to your blogger dashboard.
Step 2:
Click on the "New Post" button to create a new post or open an existing post for editing.
Step 3:
Read the rest here: http://www.sdknaija.com/2013/11/how-to-set-custom-url-for-blogger-posts.html