Spanish is a member of the Romance family of languages. They are called Romance languages not for being romantic, (which they are!) but for originating from Rome where Latin was spoken. All modern forms of these languages originated from a later form of Latin called Vulgar Latin spoken in the 7th through 9th centuries. To show the similarity between Romance languages here are a few examples of the word for sun:
soleil (French), sol (Spanish), sole (Italian), sol (Portuguese), soare (Romanian)
Today there are more than 850 million native speakers worldwide of Romance languages. The six most widely spoken are Spanish with around 350 million native speakers, Portuguese with around 230 million native speakers, French with around 70 million native speakers in France and another 50 million 2nd-language speakers in former colonies throughout the world, Italian with around 64 million native speakers in Italy and 15 million in other countries, Romanian with around 24 million native speakers and Catalan, spoken on the eastern coast of Spain, with around 12 million native speakers.
Many of the major Romance languages have offshoots. For example, French has Occitan, Spanish has Galician and Italian has Sardinian to name but a few. As it is difficult at times to distinguish between a dialect and a distinct language, estimates of the number of Romance languages varies anywhere between two and four dozen. All of these languages are similar in vocabulary and grammar and once you speak one fluently you can learn others with relative ease. That said, some are more closely related than others. For example Spanish, Portuguese and Italian can at times be mutually intelligible whereas Romanian, which has been heavily influenced by its neighbouring Slavic languages, is quite different.
Romance languages, in particular French and Spanish, are among the most commonly studied second languages in the world. Though French does not hold the status it once did, it is still used as a lingua franca in many nations throughout the world especially in its former colonies in Africa and the Middle East. Spanish is in third place worldwide for number of speakers, after English and Mandarin, and is one of the world’s most widespread languages as it is an official language in 21 nations.
For a map of Romance languages visit this link.
In addition to your main textbook, supplemental materials can be very helpful in meeting your language goals. These materials can take the form of reference books, grammar books, graduated readers, CDs and DVDs. The following suggested titles may be found at your local library, bookstore or for purchase online. I also have a lending library that carries some of these titles for the use of my clients.