I think you are asking for redirect one URL to another URL on your Blogger Blog. You can do it easily with the help of Custom Redirects features provided by Blogger.
Just visit blogger.com/home and go to the setting tab of your blog.
Now, click on Search preferences where you will find an oprion "Custom Redirects" under Errors and redirections heading.
NOTE: Both URLS (Source and destination) should not contain your Blog Domain Name (blog address).
Example:
Source (From) URL is http://www.example.com/year/month/something-old.html
Destination (To) URL is http://www.example.com/p/something-new.html
Now you should use these URLS:
Source (From) URL is /year/month/something-old.html
Destination (To) URL is /p/something-new.html
If you want to create a demo page like demo.example.com/url-address.html in blogger blog then you may create a sub-domain with the help of your domain provider.