Short answers, pulled from the story.
The Soviet Union issued ultimatums to Estonia on the 16th of June 1940 while Lithuania received its ultimatum on the 14th of June 1940. Latvia was targeted with an ultimatum delivered on the 16th of June 1940 following similar pressure from Moscow.
Soviet forces numbered around 500,000 troops occupying all three states within days of the June 1940 invasion. Earlier agreements had already permitted 75,000 troops across the nations by the end of 1939 before the full-scale occupation began.
The Independent Signal Battalion fought back against Soviet forces on Raua Street in Tallinn until sundown on the 21st of June 1940. The engagement left two dead Estonians including Aleksei Männikus and Johannes Mandre before the rest of the Defence Forces surrendered under government orders.
Deputy Commissar of Foreign Affairs Dekanozov went to Lithuania while Vishinski represented the Council of Ministers in Latvia. Regional Party Leader Zhdanov arrived in Estonia to oversee the transition and force existing presidents to resign by mid-1940.
Around 130,000 citizens labeled enemies of the people were systematically removed from their homes under the Serov Instructions. These deportations began in June 1941 under new Soviet governments installed earlier that year to break resistance before German forces arrived.