Hey Nicolás. All templates come with instruction manuals / documentation files on how to use the included features, but these will not teach you how to use the languages used ( for example HTML, CSS, JS, PHP ). If you are a basic user with minimum knowledge of the languages described in the item, you can attempt to edit it. The author can help you out with features, but authors aren’t obliged to fully build your end-product as per your requests.
In the situation where you are completely unable to edit / use the product, you can still purchase it, but I strongly recommend contacting the author first, and asking if they provide freelance services. Most authors have great prices in building their template in an end product.
If however, the author is unavailable, there is always the possibility of contracting a freelancer from Envato Studio ( https://studio.envato.com/ ) to build your end imagined product using the purchased item, or, if you’re interested in learning exactly how the languages used in the item work, you can subscribe to tutorials to learn more about them using Envato Tuts+ ( https://tutsplus.com/ )