The Spanish vowel i is pronounced much like the "ee" in "bee" or the "ea" in "neat" although perhaps a bit shorter.
It is not pronounced like the "i" in "fir," "fit" or "fire."
The i has approximately the same sound wherever it appears in a word. However, when it is followed by a stressed vowel, it combines with the following vowel to sound something like the "y" sound in a word such as "yellow" (if you listen carefully, you may notice in English that the "y" sound starts out with an "ee" sound). For example, the word bien sounds something like "byehn" would.
The Spanish y, which isn't used very often, is pronounced the same as the i. Except in a few words of foreign origin, it either comes before a stressed vowel or appears at the end of a word.
Words and phrases used by native speakers in our brief audio lesson on the i sound are "hijito," "buenos días, señor," and "muy bien, gracias."