Step 1. Complete you new entry and don't forget to publish it.
Step 2. Go to this URL.
Step 3. You will see this form. This is where you need to go back to your latest blog entry and get the URL for that particular entry. Once you got the URL from your blog, paste it to 'URL to like' in the form. Fill in the rest accordingly then click 'Get code' button at the bottom of the form.
Hope this helps!
Btw, the code is for each specific blog entry. So you have to repeat the same process for each and every new entry on your blog. (If you want to)