Letters are like building blocks to make words. When we talk (either in Spanish or English) we use composite of letters and sounds to make new words. In fact, as we combine letters, we phonetically pronounce words.
In Spanish, we use syllables, in many combinations, to form one, two, three, or even four syllable words. In many instances, Spanish syllables can be either weak or strong depending on how vowels are combined.
By learning the Spanish alphabet, you know the basic pronunciation of many words. And, if you know many words in Spanish, you increase your vocabulary. As you read more and more Spanish books, you will recognize the word in print.