Is it like the 'j' in English 'jet' or what? Which is the official sound: the English 'y' or the 'j' sound? How is it? I'm told the letter Y is pronounced in Spain as the J in 'jet' in English.
The short answer is: there is no single pronunciation for the letter y.
The longer one is, it varies regionally and by context.
It can be pronounced like a softer version of the "j" sound in "jet" in words like yegua, yoyo, and like the i sound in "bin" in words like hoy, maya.
Then, in some regions of South America (mainly Argentina), it is pronounced like a mixture of "j" and "sh".
In European Spanish the letter "y" is not pronounced like the english letter "j" , although with some Latin American accents it sounds more like the French pronunciation of "j" in "je suis". From my experience Spanish speakers from Spain find it very difficult to pronounce the "j" sound in the way English speakers do when saying jet, jeans or bridge.
The "y" sound is made as if you were pronouncing it in English (eg. in the word yurt), but you start with your tongue flat against the roof of your mouth, a little behind your front teeth. Try saying "and you" quickly; the "dyuh" sound – with an almost silent "d" at the beginning – is what you're looking for.