I wouldn't say so. You certainly don't pronounce it like in, for instance, "gatto", but it's not silent either. It's hard to explain since there is no such sound in English. Put some words like "taglio" in Google Translate and listen carefully. A tip: To pronounce it, your tongue also has to touch the top of your mouth, but further to the back, without touching your teeth. Hope this helps.
yes, you have to stick your tongue to the roof of the mouth, the air goes out from the lateral parts of the mouth. The lips are not so opened (they're like doing the "e" but the inside is completely different). Some example can be found here (go to 6:40) https://www.youtube.com/watch?v=uHEYrEr1lsQ
The Italian "gl" is pronounced like the "ll" in the Spanish words "pollo" and the "il" in familia". In English, it sounds like the "y" in "yet". The site Glass-paper recommended is excellent. From another YouTube site, I learned that in Rome and the surrounding area "gli" is prounounced like "yee/yi". The man on the site Glass-paper recommends pronouncing it a slightly different way, which I can't put my finger on yet. Maybe like TheGandalf writes: "lyee".