Evolutionists believe that all life evolved to its present forms through natural selection. The critters who had gained useful traits through mutations survived to breed (or bred more often) than competing organisms.
Creationists believe that the first chapters of Genesis are literally true, that God created the world in six days. Though some of the folks working in creationist circles are competent, legitimate scientists, creationism can best be described as religion criticizing Darwinism.
Intelligent design has to do with scientists finding structures in organisms that appear to disprove Darwinism because they have "irreducible complexity." They couldn't have evolved into their present form because they wouldn't have worked (much less given the ancestor critter advantages) if they were simpler. Michael Behe, who wrote the book "Darwin's Black Box" and started the whole ID ruckus, compared them to mousetraps, because if you remove any one part from a moustrap it's useless. One of the systems he cited was blood clotting; if any particular component chemical is absent, the system doesn't work at all. Ergo, these systems must have been designed by an intelligence, or they must have occurred naturally in some way other than simple forms becoming more complex via natural selection. Either of those would disprove the current Darwinian model.
IDers are often accused of being creationists, but ID is science criticizing science, which is why it is so feared.
Let me know if you have any other questions. I'll leave you with a chart of the coagulation cascade in blood clotting:
