Another one of the great things about Path of Exile is that the developers are always introducing new things into the game to keep it fresh and interesting. Recently with The Awakening expansion, Grinding Gear Games had introduced something called Divination Cards that now has players digging in. They make for a more seamless gameplay experience by letting you farm for specific unique Path of Exile items and even currency items, so you do not have to go into every farming run blind and only hoping for scraps. With Divination Cards, every farming run seems to have a purpose again.
Divination Cards were created by members of the Path of Exile community as part of the supporter pack bonus for The Awakening expansion. A card includes the theme, the item you're bound to receive, card art, and flavor text, which were all decided by a community member. These cards were designed for what is known as deterministic farming, which is basically farming in a specific way according to a specific Divination Card in order to get a specific item. It is pretty much a more motivating way to farm in the game other than just aimlessly grinding away without much rhyme or reason.
The best shot players used to have in getting a specific item was to farm enough currency POE items to actually purchase the item from someone else. Along the way, perhaps some players get lucky and get exactly what they want, but that is quite a long shot for most people since the chances of that actually happening are very slim. But with Divination Cards, you get to turn those odds a bit more to your favor and actually get the item you want through farming.
For example, you get a card that says "axe" on it. That means you can get any kind of unique axe when you farm with that card, and that is good if the particular item you are looking for happens to be an axe as well. This works because Divination Cards themselves are dropped in specific locations. Whatever location that may be depends on the Divination Card itself; some cards have only one location each, while others can be dropped in different locations.
The point of this is that the old alternative of randomly mapping and farming bosses yields an even smaller chance at getting good items than through Divination Cards. If what you are looking for happens to have a Divination Card for it, then you are in luck and you could even build up a set of those cards for more chances of getting what you want. The Path of Exile wiki site should have the locations for these Divination Cards.
As for how many of each Divination Card you need, you can see right there on the left side of the card. If it says 5, then you need five of those cards to complete a set. The level of item you can get with this method should be equivalent to your current character level, right up until level 82.