Romance languages are notoriously difficult for English-speakers to learn because of the gender of each noun. Not only do you have to learn a new word such as "libro" but you also have to remember that it's "el libro" which is also a "masculine" noun in Spanish, meaning that any adjective you attach to it has to be in masculine form as well.
What you might not have known, is that some words change meaning based on the article/gender that you use with it.
Here are some examples:
Spanish
el capital = financial capital/money la capital = capital city
el orden = order/sequence la orden = religious order or command
el cura = priest la cura = cure/treatment