English speakers generally find the pronunciation of Spanish vowels fairly easy. Close approximations of all their sounds exist in English, and, with the exception of the E and the sometimes silent U, all the vowels have basically one sound.
The main thing to keep in mind is that in Spanish the vowels' sounds are generally more distinct than they are in English. In English, any vowel can be represented by what's known as the schwa, an unstressed vowel sound such as the "a" in "about," the "ai" in "mountain," and the "u" in "pablum." But in Spanish, such an indistinct sound isn't used. Although, as in most languages, the sounds of the vowels can vary slightly with the letters before and after them, in general the sound remains the same regardless of the word it's in.
Now, the two vowels whose sound can change:
- A is pronounced similarly to the "a" in "father" or the "o" in "loft." Examples: madre, ambos, mapa. There are some speakers who sometimes pronounce the a something halfway between the "a" in "father" and the "a" in "mat," but in most areas the first sound given is standard.
- I is pronounced similarly to the "ee" in "feet" and the "e" in "me," although usually a little briefer. Examples: finca, timbre, mi.
- O is pronounced like the "oa" in "boat" or the "o" in "bone," although usually a little briefer. Example: teléfono, amo, foco.
Diphthongs and triphthongs: As in English, two or three vowels in Spanish can blend together to form a sound. The sound is basically the sound of the two or three vowels rapidly pronounced. For example, the u when followed by an a, e, i or o ends up sounding something like the "w" in "water." Examples: cuaderno, cuerpo, cuota. The ai combination sounds something like the sound of "eye." Examples: hay, airear. The i when followed by an a, e, i or u sounds kind of like the "y" in "yellow.": hierba, bien, siete. And other combinations are possible as well: miau, Uruguay, caudillo.
- E is generally pronounced like the "e" in "met" when it is at the beginning or within a word. It is pronounced similarly to the Canadian "eh," kind of a shortened version of the "é" in the English "café," when it is at the end of the word. Sometimes it can be somewhere between those two sounds. It's not quite the sound of the English letter "A," which if pronounced slowly often has an "ee" sound at the end, but closer to the "e" of "met." Keep in mind that even when it's at the end of the word, in a sentence it may sound more like the "e" of met. For example, in a phrase such as de vez en cuando, each e has approximately the same sound. Examples: café, compadre, embarcar, enero.
- U is generally pronounced like the "oo" in "boot" or the "u" in "tune." Do not pronounced it like the "u" in "uniform." Examples: universo, reunión, unidos. In the combinations gui and gue, as well as after q, the u is silent. Examples: guía, guerra, quizás. If the u should be pronounced between a g and i or e, an umlaut (sometimes called a dieresis) is placed over it. Examples: vergüenza, lingüista.
The letter Y: Generally, the y is pronounced the same as it would if it were an i, as part of a diphthong. Examples: rey, soy, yacer. In some words that are derived from English and have a y at the end often retain the English pronunciation. For example, in popular songs you may hear words such as sexy and phrases such as oh baby.