Add something at the posts

Try..

if (is_page()) {
echo "This is a post page";
}

Regards

Thanks for your answer Cypher but seems to not be working
I should put it in index.php, right?

Try to re-phrase your initial question.
Where exactly do you want to show “something”?
On the main page?
On a Page? – for this see Cypher’s code
On a single post view?

I want to show it on a single post view

In that case you’ll need if is_single.
Learn more here > Conditional_Tags.

Thanks Cypher and moshu ??
it works now