A summary from the US State Department, culled from their most recent "Patterns of Global Terrorism" report (available online at www.state.gov). Pardon the cut and paste writeup, but I found this to be of value. NB: State uses the less popular transliteration of the group name.
Description
Established by Usama Bin Ladin in the late 1980s to bring together Arabs who fought in Afghanistan against the Soviet invasion. Helped finance, recruit, transport, and train Sunni Islamic extremists for the Afghan resistance. Current goal is to establish a pan-Islamic Caliphate throughout the world by working with allied Islamic extremist groups to overthrow regimes it deems "non-Islamic" and expelling Westerners and non-Muslims from Muslim countries. Issued statement under banner of "the World Islamic Front for Jihad Against the Jews and Crusaders" in February 1998, saying it was the duty of all Muslims to kill US citizens--civilian or military--and their allies everywhere.

Activities
Plotted to carry out terrorist operations against US and Israeli tourists visiting Jordan for millennial celebrations. (Jordanian authorities thwarted the planned attacks and put 28 suspects on trial.) Conducted the bombings in August 1998 of the US Embassies in Nairobi, Kenya, and Dar es Salaam, Tanzania, that killed at least 301 persons and injured more than 5,000 others. Claims to have shot down US helicopters and killed US servicemen in Somalia in 1993 and to have conducted three bombings that targeted US troops in Aden, Yemen, in December 1992. Linked to the following plans that were not carried out: to assassinate Pope John Paul II during his visit to Manila in late 1994, simultaneous bombings of the US and Israeli Embassies in Manila and other Asian capitals in late 1994, the midair bombing of a dozen US trans-Pacific flights in 1995, and to kill President Clinton during a visit to the Philippines in early 1995. Continues to train, finance, and provide logistic support to terrorist groups in support of these goals.

Strength
May have several hundred to several thousand members. Also serves as a focal point or umbrella organization for a worldwide network that includes many Sunni Islamic extremist groups such as Egyptian Islamic Jihad, some members of al-Gama'at al-Islamiyya, the Islamic Movement of Uzbekistan, and the Harakat ul-Mujahidin.

Location/Area of Operation Al-Qaida has a worldwide reach, has cells in a number of countries, and is reinforced by its ties to Sunni extremist networks. Bin Ladin and his key lieutenants reside in Afghanistan, and the group maintains terrorist training camps there.

External Aid
Bin Ladin, son of a billionaire Saudi family, is said to have inherited approximately $300 million that he uses to finance the group. Al-Qaida also maintains moneymaking front organizations, solicits donations from like-minded supporters, and illicitly siphons funds from donations to Muslim charitable organizations.