Pronouncing Spanish vowels is simple. Each vowel has only one way to be pronounced, and it will be pronounced that way in every word. Unlike English, there are no silent vowels in Spanish, although some vowels will slur together to create a single sound. These vowel combinations are called diphthongs.
You should be careful not to let your vowels become dipthongs when speaking Spanish. Spanish vowels are shorter, sharper, and more crisp than English vowels; therefore, Spanish vowels produce only one, constant sound. Also, the English schwa sound doesn't exist in Spanish although it is quite common in spoken English. For example, Spanish never has sounds like “pencil” [pεnsl]. The last syllable of “pencil” contains the relaxedschwa sound. To further illustrate this notion, the word banana is the same in Spanish and English. However, in English the last syllable is the schwa  sound, and in Spanish all of the a's are open vowels that are pronounced exactly the same in all three syllables.
Vowel sounds and spellings
The few Spanish words that are common in English can serve as models for your pronunciation. Pronounce the word “taco.” The letter a is always pronounced like it is in taco. If you have ever heard a person speaking with a heavy Spanish accent, you may have noticed that they usually say a word like “hat” or “can” sounding more like the English words “hot” or “con.” That is because they are saying the letter a the only way it can be said in their language.
The letter o is also consistently pronounced like it is in taco. You may notice that the o is shorter in Spanish and doesn't end in a wa at the end.
Another word we have learned from the popularity of Mexican food is burrito. The Spanish vowels u and i are always pronounced like they are in the word burrito.
The only vowel left to master is the e. It is always pronounced like the e in café (even when there's no accent on the e). To see how well you're learning, go back and make sure you pronounce the a in café correctly. It should sound like the a in taco.
Notice that the e at the end of café is not silent as it in the English word “cake.” Remember that there are no silent vowels in Spanish (except for the u in qu and gu followed by e or i), so be careful of cognates that end ine, and remember to pronounce it at the end.
The letter y is a vowel only when it stands alone or when it is at the end of the word. It is pronounced like the i in “burrito” when it is a vowel, as in ley, for example . As a consonant, the Spanish y sounds just like “yellow” in English, as in yo.
The easiest vocabulary words to learn are also the trickiest to pronounce. A lot of Spanish words look similar to English words, and some are even spelled the same. But, as discussed earlier under “Cognates,” these words are never pronounced exactly like their English equivalent. Also, a Spanish word that does sound like an English word will probably be spelled differently in Spanish to maintain the rules of their language. When you recognize a cognate and immediately determine its meaning, it is natural to just say the English word.
Here's one good way to eliminate the urge to simply pronounce a cognate in Spanish the same as you would in English. Practice by pronouncing all English words as if they were Spanish. At the end of the unit, this example will make more sense, but imagine when you see the English word “imagine” that you pronounce it “ee‐mah‐hee‐nay” because that's how the letters would be pronounced in Spanish. Later, when you learn the wordimagina you will be prepared to say “ee‐mah‐hee‐nah” almost perfectly.
The strong vowels are a, e, and o. When two strong vowels are used together in a word, the result is two separate syllables with both vowels strongly pronounced. If one of the strong vowels is used beside a weak vowel, the resulting single syllable, called a diphthong, is a slur of the two vowels, with the stronger vowel the only one that is clearly heard.
The weak vowels are i and u. Remember that in the battle of the weak vowels, the last one gets stressed. The u creates the sound of an English w. When the i is used with a stronger vowel, the i sounds like the consonanty in both languages.