King of Avalon almost always has one or two seasonal events being active. At this time the St. Patrick's Day Event is one of them. This guide explains how the event works.
During the duration of the event you get a chance of receiving Leprechauns when slaying monsters and rallying Barbarian Camps, and Shamrock when gathering resources. These Leprechauns and Shamrock Items show up in your inventory where you can use them to get prizes.
You do not have to do anything else as what you normally have to do anyway to get Leprechauns, whenever you have Stamina you should kill Monsters or rally Barbarian Camps.
You have a chance at receiving Shamrock while gathering resources, which you will be doing a lot anyway, so nothing else needed to be done to get this item either.
You get your prizes by selecting the Leprechauns in your items and clicking Use. Prizes I have received include: 5K Food Items and Materials (Animal Hide, Cerussite, Pine, Bronze, Cypress, Galena, Horn, Emerald, Amber). For the Materials the 4 Standard Materials (Animal Hide, Cerussite, Pine, Bronze) had a lot higher drop rate than the other materials.
You get your prizes by selecting the Shamrock in your items and clicking Use. Prizes I have received include: 100 Lord EXP, 100 Dragon EXP, 10 Assault Power, 10 Guardian Power, 2500 Dragon Spirit EXP, 1k Wood, 24 Hour Iron Mine Boost, 24 Hour Silver Mine Boost, 5m Speedup, 50m Speedup.
There is not much to it, just do what you normally do and collect the extra prizes. If you have any questions, or comments, let me know in the comment section.