Short answers, pulled from the story.
Vladimir Putin signed accession treaties with four pro-Russian leaders on the 30th of September 2022. The signing ceremony occurred in the Grand Kremlin Palace in Moscow within the St. George Hall.
The four oblasts originated from Yekaterinoslav, Kherson, Taurida and Kharkov Governorates before becoming part of the Soviet Union. Territory in the Kherson and Zaporizhzhia Oblasts fell under Russian control during the campaign that began in February 2022.
Russia held about 60% of Donetsk Oblast while most of Luhansk Oblast remained under their control. Almost all of Kherson Oblast was occupied by Russian forces and about 70% of Zaporizhzhia Oblast fell under military command.
Only North Korea and Baathist Syria have recognized the move as an exception to international law. A United Nations General Assembly resolution passed on the 12th of October 2022 had 143 nations voting in favor against only five.
On the 19th of October President Vladimir Putin declared martial law in the annexed areas. Legislation allowed for bans on public gatherings and other widespread restrictions on personal liberty.