Haredi Judaism, Hasidic Judaism, and Orthodox Judaism are all names for different religious movements within the Jewish faith. The three can be looked at as a family, with Haredi Judaism existing as a subset of Orthodox Judaism, and Hasidic Judaism existing as a further subset of the subset. The difference is really one of specific beliefs, and a matter of degree, rather than any sweeping large generalization. All three sects agree on the importance of God's word and laws, but they choose to adhere to those laws in slightly different ways.
Orthodox Judaism is largely defined by a firm belief that the Torah and the laws contained within it are of divine authority, and therefore should be subjected to a strict interpretation and observance. Members believe that the Torah comprises the laws that shall govern the covenant made by God with the Children of Israel. Orthodox Judaism is a large branch of Judaism, and until fairly recently, most Jews could be said to be Orthodox.
It wasn't until the Reform movement that large numbers of Jews departed from more traditional Orthodox teachings. Reform Jews, who focus on the concept of ethical monotheism, believe that only the ethical laws of the Torah are binding. Additionally, they believe that other laws, like those laws in the Talmud, were products of their time and place, and so it was not necessary to treat them as absolute.
In the late-19th and early-20th century, the Orthodox movement itself underwent some changes. Newer Orthodox Jews tried to integrate the teachings of the Torah into modern life, making some concessions and adaptations to better mesh with contemporary technologies and practices. At the same time, other Orthodox Jews rejected most modern movements, and looked warily on any reinterpretations of Jewish law to make it fit into a modern context.
These "Ultra-Orthodox" Jews became known as Haredi Jews, although both of these terms are considered negative in some circles. The term is also sometimes spelled Charedi or Chareidi in English. It is important to note that members of this group do not reject the modern world or technologies entirely, but they treat adaptations of Jewish law to fit that world as very serious. Most of the differences between Haredi and Orthodox perspectives have to do with decisions of oral law as to how the Torah should be applied to a modern situation. In many broad senses, the two groups tend to agree, and it is more in the specifics that things begin to diverge.
Hasidic Judaism is a movement within Haredi Judaism that focuses on the study of the spiritual and joyful elements of the Talmud. It has its roots in the anti-Kabbalah movements of the 13th century. Hasidim focus on a loving and joyful observance of the laws laid out in the Torah, and a boundless love for everything God created. Members live in small, separate communities, and are often noted for their distinctive clothing.
This movement began in the 18th century by Rabbi Israel ben Eliezer, later known as Baal Shem Tov, the Master of the Good Name. Hasidic Judaism sets aside the earlier emphasis on studying the Torah from an academic perspective, and instead exalts the experience of it at all moments. Within the movement there are a number of sects, including the Satmar, Belz, Ger, Sanz, Puppa, Spinka, and Lubavitch.