Finland was engaged in a separate war with the Soviet Union prior to the German invasion the Soviet Union in 1941. The Winter War, as it is called lasted 3 months from November 1939 to March 1941, and Finland lost about 11% of it's land according to the Moscow Peace Treaty, signed in March 1940.

In preparation for Operation Barbarossa in June, Germany allied itself with other nations, Hungary and Romania being two prime examples, to give it an edge against the Russians. Finland, looking to regain some lost territory, agreed to fight the Russians along side Germany, this is know as the Continuation War.

This lasted for over 3 years, from June 1941 until September 1944. The fighting mainly took place in the Karelia region, near Leningrad in Southern Finland. Finland also received quite a lot of military equipment from Germany. However Finland never signed the Tripartite Pact, so it's actually wrong to call it one of the Axis Powers.

An armstice between Finland and the Soviet Union was signed on the 19th of September in Moscow, bring Finland's part in the war mainly to an end. Unlike most of Germany's allies, Finland did not lose independence after the war. But it was a hard blow in terms of reparations and Finland's reputation, which became apparent during the Cold War.

I hope this sort of answered your question, this my first time answering a question like this.