Fresh hop beers are made when green hops are packed straight from the farm just before they reach the kiln (the drying process which helps to preserve the hops prior to pelleting).
Wet hops need to be used differently than dried hops. First, they must be used as soon as possible, as they will go bad very quickly. You also need to use much more by weight than for dried hops. Each year brewers engage in a feat of logistical gymnastics to get the hops into their beer as close to harvest as possible.
The flavour and aroma of fresh, wet hops, is impossible to achieve through dried hops. We only get these fresh hop beers once a year, and once they're gone, they're gone. So if you want to try the unique character of fresh, wet hops, get in now.