Short answers, pulled from the story.
Khalq was a far-left faction of the People's Democratic Party of Afghanistan, drawing its name from the Dari word for "the masses." Its membership was primarily Pashtuns from rural backgrounds, and its leaders advocated class struggle and a mass organization approach to bring about political, economic, and social change.
The de facto leaders of Khalq were Nur Muhammad Taraki, who led the faction from 1967 to 1979, and Hafizullah Amin, who led it in 1979 before being killed in the Soviet intervention in December of that year.
Khalq seized power through the Saur Revolution on the 27th of April 1978, a military coup carried out almost entirely by Khalqist army officers and air force units. Colonel Mohammad Aslam Watanjar commanded the ground forces that took Kabul, while Colonel Abdul Qadir led the air assault on the Royal Palace that killed President Mohammad Daoud Khan.
The Soviet Union intervened in December 1979 after the Khalqist regime, under Hafizullah Amin, ignored repeated Soviet advice to moderate its radical land reform policies, include Parchamis in government, and show respect for Islam. Soviet intelligence forces killed Amin and replaced him with the Parchami leader Babrak Karmal.
Khalq and Parcham split in 1967 over a fundamental disagreement on revolutionary strategy. Taraki believed Afghanistan could follow a classical Leninist path with a disciplined working-class party, while Karmal felt the country was too undeveloped for that approach and required a broad national democratic front first.
After the Soviet intervention, many Khalqi officers mutinied against the Parchami-dominated government and some assisted the Mujahideen. Following the collapse of Najibullah's government in April 1992, former Khalqists joined or allied with the Taliban or Mujahideen warlords; Khalqi pilots flew Taliban aircraft and crews operated Soviet tanks and artillery during the Afghan Civil War.