How do i make a portfolio picture link to another website in Wordpress?

<a href="http://examplesite.com" target="_blank">
   <img src="image.jpg" alt="Something about your image">
</a>

You could just hard code it in like that.

A better way would be to use a plugin like Advanced Custom Fields to create a field for the website in the WordPress backend. Then you can get that URL and store it in a variable, which would then allow you to loop through all the websites you've built and insert the URL dynamically.

For example,

<?php

<?php if ( have_posts() ) : while ( have_posts() ) : the_post(); ?>

 $image = get_field('image');

$url = get_field('url'); 

$description = get_field('description');

    <a href="<?php echo $url;?>" target="_blank">
      <img src="<?php echo $image; ?>" alt="<?php echo $description; ?>">
    </a>

<?php endwhile; else : ?>

    <p><?php _e( 'Sorry, no posts matched your criteria.' ); ?></p>

<?php endif; ?>

The basic idea here is that the WordPress loops fetches all the posts you've done for your Portfolio custom post type then goes through the above code and dynamically inserts the data you've inputted in the WordPress backend.

Some resources:

http://www.advancedcustomfields.com/resources/image/

http://codex.wordpress.org/The_Loop

https://wordpress.org/plugins/custom-post-type-ui/

You should also check out Zach's WordPress courses if you haven't already. Hope that helped.