Not much. According to Catholic Online:
Patrick was born around 385 in Scotland, probably Kilpatrick. His parents were Calpurnius and Conchessa, who were Romans living in Britian in charge of the colonies. As a boy of fourteen or so, he was captured during a raiding party and taken to Ireland as a slave to herd and tend sheep. Ireland at this time was a land of Druids and pagans. He learned the language and practices of the people who held him.
After his captivity, Patrick felt the need to return to Ireland and preach. Over the next forty years, he worked in Ireland, sharing the Gospel to those who held him in captivity for a mere six years.
Biography adds this bit:
The Episcopal Church annually honors St. Patrick with the celebration of St. Patrick’s Day on March 17, which falls during the Christian season of Lent. For more than 1,000 years, the Irish have observed St. Patrick’s Day as a religious holiday. Traditionally, on St. Patrick’s Day, Irish families would attend church in the morning and celebrate later—including eating a traditional meal of cabbage and Irish bacon.
Irish and drinking go well together, so it really isn’t a leap to head to drinking green beer. Americans have embraced that practice more than anyone else. My personal favorite story is that the Irish would drink a shamrock in whiskey. Of course, shamrocks being the symbol of the Trinity. St. Patrick used the natural foliage to convey the message to the Irish.
Regardless of the reason, there will be green beer consumed this weekend. Be safe when you do so consume.