I regret seeing that many people who have posted above have not actually answered your question, but have instead posted propoganda promoting their particular side of the debate. I will give you straightforward definitions of each of these terms:
"Evolution" is a scientific theory asserting that populations of organisms change over time. It says that generation after generation, organisms that have traits that help them survive will reproduce more often, and therefore pass those traits on to their offspring. In this way, species will slowly change in order to better adapt to their environment. The theory also says that it is through this process that all present day life on earth arose from a common ancestor, much the same as the way your family tree shows you and all your brothers, sisters, and cousins to arise from the same grandparents. Proponents of evolution often cite advances in genetics, observations from current ecosystems, and many fossils from the fossil record to support the theory.
"Creationism" is the idea that God created the earth, and all of the life forms on it. It asserts that all the creatures on the earth, including humans, were separately designed by God, and most people who believe this idea are very much opposed to the idea of evolution. There are many different forms of creationism, so it is really a blanket term for many different variations on this belief, but the common form of creationism that many Christians identify with is that God created the earth, humans, and animals about 6000 years ago. About 4000 years ago, there was a global flood, during which Noah and his family saved a male and female of each species of animal and carried them on the Ark, and present day life arose from the branching out of humans and animals that were saved on the Ark. Proponents of creationism believe that the bible gives a literal account of human history, and that much of the scientific evidence allegedly supporting evolution is flawed.
"Intelligent design" is the idea that some intelligent being designed life, rather than life evolving through time. Proponents of this idea cite examples of complex structures in living things that they feel could not have evolved via natural, mechanistic processes but instead require some sort of designer who knew how to build biological systems. The idea does not specify that the designer is God, but its basic tenets are extremely similar to creationism. It is a more recent term that has been used only in the past decade or so, and has been alleged to be nothing more than creationism repackaged with a fancier title in order to make it easier to get into public school science curriculums.
I hope this answers your question. There many websites on each of these topics that should be easy to find with a Google search, and will give you a lot of detailed information.