In Spanish, words that contain -gue and -gui are pronounced with a hard g sound like you hear in the English words gate, good or again, and in the Spanish words guerra and guisante. Without the u they would have the soft g sound which is very close to the pronunciation in Spanish of the letter j which in most of the Spanish peninsular is a similar sound to the gutteral ch sound in Scottish words like loch and in much of Latin America is closer to a very aspirated h sound of the English words holly or happy - you can hear it in Spanish words like gente or gimnasio.
Let's look at some examples with gue and gui :
But there are a few words in Spanish containing -gue, -gui that are pronounced differently. The g is still a hard g but the sound of the u needs to be pronounced. To indicate this special pronunciation the written word uses the orthographic symbol called a "diéresis" in Spanish (diaeresis or dieresis in English). This symbol looks like two dots above the letter ü. Some examples of words using a dieresis are:
Listen how the pronunciation is completely incorrect if we do not include the dieresis:
incorrect
correct
Note that in Spanish the sounds formed by ga, go and gu are called "g suave" and those formed by ge and gi are called "g fuerte" - which is the opposite of how these sounds are described in English (hard g and soft g respectively).
