Oke, go to blogger dashboard -Edit HTML -Check Expand Widget - and find the code below:
<b:if cond='data:top.showAuthor'>

Place following code before the code above

<b:if cond='data:post.url'>
<a expr:href='&quot;http://www.facebook.com/share.php?u=&quot; + data:post.url'><img alt='www.tips-fb.com' border='0' src='http://i15.photobucket.com/albums/a398/syilpid/share_on_facebook_2.png'/></a>
</b:if>

The code above will appear be like this button:



If you want to using another button , can use these code below :



<b:if cond='data:post.url'>
<a expr:href='&quot;http://www.facebook.com/share.php?u=&quot; + data:post.url'><img src="http://i15.photobucket.com/albums/a398/syilpid/share_on_facebook_4.png" border="0" alt="www.tips-fb.com"></a>
</b:if>




<b:if cond='data:post.url'>
<a expr:href='&quot;http://www.facebook.com/share.php?u=&quot; + data:post.url'><img src="http://i15.photobucket.com/albums/a398/syilpid/share_on_facebook_3.png" border="0" alt="www.tips-fb.com"></a>
</b:if>

Or use your own text , for example : "Share On Facebook"

<b:if cond='data:post.url'>
<a expr:href='&quot;http://www.facebook.com/share.php?u=&quot; + data:post.url'>Share on Facebook</a>
</b:if>

End...