When you first began to learn English, it's unlikely that you can remember how it was, but chances are quite high that you learned to speak the English language by hearing what your parents said to you and repeating back words or phrases to them.  You copied what you heard as best you could and probably received countless gentle corrections and  lots of encouragement and praise along the way.  It would not have been until much later, maybe as much as five or six years, that you began to read the English language and even longer before you had to begin the task of studying English grammar.

Because you were in a setting where you probably heard only English being spoken, unless of course you were raised in a multi-lingual family or other special circumstances.  Over time you just assimilated the words that were being spoken and eventually they began to be understood.  After time, you could not only understand English, but could make yourself understood in English both oral and written.

Learning Spanish through a Spanish immersion course is very like the circumstances where you learned to speak your native language. You spend time in a Spanish-speaking country and are totally surrounded by the language and the culture so you start to absorb the language in the same way that you absorbed your native language. Learning Spanish by immersion usually adds daily classes which are focused on placing you in situations where you have to quickly learn how to cope.  For instance, you may be faced with shopping for food or other necessities or you may need to travel from one location to another. 

Learning Spanish by immersion courses often place you in a home with a local family thus providing additional learning advantages.  Just as when you were learning English as a toddler, you will be in a setting where only Spanish is spoken at all times.  You will share meals and other situations over and over and through time and repetition, the words and phrases used will stay with you.  You can force yourself to respond haltingly at first, but your confidence will build as you correct your errors and go on.

Learning Spanish language skills will improve with immersion style classes, but your appreciation of the culture of the country where you are staying will soar.  You will make new friends with the host family and learn to like some of the activities they enjoy.  If you are fond of some particular activity, why not select your study location with that in mind. For instance if you are learning Spanish in Barcelona, you can watch the games in the famous stadium there.  If you like the tango, why not choose a language school in Buenos Aires.  People who love history can study Spanish in San Juan, Puerto Rico and gain the benefit of the Old Town there.

For learning Spanish, or any other second language, there is no question but what total immersion is the preferred learning method.