Short answers, pulled from the story.
The Sąjūdis Initiative Group formed on the 3rd of June 1988 when thirty-five people gathered inside a hall at the Lithuanian Academy of Sciences. Most of these founders were artists rather than career politicians, with seventeen members holding membership in the Communist Party.
Sąjūdis organized its first massive gathering at Soviet Square near the Soviet Palace three days after its formation. On the 23rd of August 1988, roughly two hundred fifty thousand protesters assembled to condemn the Molotov Ribbentrop pact.
Vytautas Landsbergis became chairman of the council in October 1988 as a professor of musicology who did not belong to the Communist Party. He later won an absolute majority of one hundred one seats out of one hundred forty-one in the Supreme Council.
On the 23rd of August 1989, two million people formed a human chain stretching six hundred kilometers from Tallinn to Vilnius during the Baltic Way. This event drew international attention to Baltic aspirations for independence from the Soviet Union.
Popularity waned because economic crises weakened support for the movement's agenda while rural regions withdrew backing due to ignored kolkhoz workers' interests. The group failed to maintain unity across diverse political beliefs after reform communists and liberal intellectuals left about a month after independence was gained.