I assume you mean the Great Irish Famine caused by the failure of the potato crop between 1845-1852. The famine was caused by potato blight, a disease which destroyed the potato crop. Since potatoes require a great deal of time to mature, once the damage was done, it was too late to plant another crop. The consequences included starvation and death, emigration, and eviction, and revolt.
Since potatoes were a staple in the Irish diet, many people died either of starvation of illnesses related to malnutrition. Estimates of the death toll vary from 500,000 to over one million. Many died from cholera, caused by drinking contaminated water.
Roughly one million people left Ireland during the famine, many of whom emigrated to the United States and Canada. Most who emigrated were younger members of families who wished for a new beginning. They generally settled in large cities, such as Boston and Philadelphia, eventually becoming a substantial portion of those cities' population.
Aside from starvation, many emigrated because they were evicted by their landlords. Many people were not eligible for public assistance, and since landlords were taxed for the land, they evicted poorer tenants with abandon. Many tenants did not take kindly to eviction, and several landlords were murdered by angry tenants.
Finally, a rebellion broke out in 1848. The rebellion failed, and most of the leaders were exiled to Tasmania off the coast of Australia.