Where to insert ACF code?

Hi,

First let me say that the Sentio theme is a very beautiful and clean theme, I’m a fan! ??

I would now like to include additional content fields using the Advanced Custom Fields plugin. I understand that I need to create the fields first, and then – in order for the page to actually display them – include the following code into the php file:
<p><?php the_field(‘field_name’); ?></p>

However, can you please advise where the best place would be to insert that piece of code?

It is supposed to be a simple additional text field below the content field.

Thanks in advance, and I am looking forward to hearing from you.

Warm Regards