I have put my forum in a subdomain. What I do is a call from the main domain so that it displays something on the main page displaying the last two posts in the forum, making only the first 20 characters of each post and with the links to the forum
How could I make that call?

Thanks

You may use the free "First page news" add-on from Downloads to display content from your forum on external pages.

There is anything that I'm doing that isn't well because ins't working
Here I put in addon_1stpagenews2.php
$path='/hsphere/local/home/c34727/foros.fotoviaje.net/'; Is it correct?
the call get throught include
<?php include ('http://foros.fotoviaje.net/addon_1stpagenews2.php');?> is it correct?

Thanks

You could alternatively try to install RSS addon for the forum and then grab the RSS feed and show its contents where you like. You can fetch RSS feeds with for example SimplePie.

How can I know it? :) It depends on what is given by getpwd() function.

You don't have to deal with PHP in that case. Use JavaScript option of this add-on, it would be much simpler for you.

Dealing with PHP include means your subforum should be on the same server as the primary site. This add-on can not be included like you did, via HTTP request.

I've just got my hands on the similar add-on and I think you don't see anything because error reporting is disabled in PHP.
But actually, you may also get this error when including PHP file from external resource:
http:// wrapper is disabled in the server configuration by allow_url_include=0