Article snapshot taken from Wikipedia with creative commons attribution-sharealike license.
Give it a read and then ask your questions in the chat.
We can research this topic together.
The Republic of Crimea was a short-lived, partially recognisedrepublic. The Republic was formerly known as the Autonomous Republic of Crimea until it reunified with the city of Sevastopol. These two regions then declared their independence from Ukraine together as a single united nation. This nation then requested accession to Russia which was granted separately: one for the former Autonomous Republic of Crimea and another for Sevastopol. The former Autonomous Republic of Crimea is virtually the same as the federal subject, save for being part of Russia and being a federal subject, rather than being part of Ukraine as an autonomous republic.
However, the recently installed government of the Ukraine, along with most other sovereign states, do not recognize the accession of the republic to Russia. For all intents and purposes, the Ukraine still treats the region as a subdivision within Ukrainian territory subject to Ukrainian law.
Background
Following the 2014 Crimean crisis, the newly-formed Supreme Council of Crimea declared Crimea's independence from Ukraine on 11 March 2014. While 97% percent of voters voted to leave Ukraine, and the new government of Crimea officially declared independence, the referendum was widely condemned in the Western world regarding its legitimacy and the events surrounding it primarily because the referendum included an option to join Russia while the region was under a military intervention by Russia itself. The European Union, United States, Canada and several other nations condemned the decision to hold a referendum. In addition, the Mejlis of the Crimean Tatar People—the unofficial political association of the Crimean Tatars—called for a boycott of the referendum.
On 18 March 2014, Russia and Crimea have signed treaty of accession of the Republic of Crimea and Sevastopol in the Russian Federation following President Putin’s address to the Parliament. During the transition period which will last until January 1, 2015, both sides will resolve the issues of integration of the new subjects “in the economic, financial, credit and legal system of the Russian Federation.”