During WWII, the USA and the USSR were members of the allied and fought against the Axis. But after 1945, their relationship changed and became unfriendly.
This unfriendly relationship between the USA and the USSR led to the event known as the cold war.
The western (the Capitalist bloc) was represented and headed by the USA but the eastern (Communist bloc) was led by the USSR or Russia.
It covered from the end of WWII, 1945 continued to the late 1980s.
Capitalists(USA) follow a free market economy and multi-party system which is the direct opposite of communism(USSR)
Communists (Socialists)-follow a command economy and single-party system.
Both powers were interested in expanding their respective ideological influence and interested to control the world. This situation led the world into a bi-polar political system.
The bi-polar is a political system of world order in which the majority of international economic, military, and cultural influence was held between two states the USA and the USSR
Cold War was not a direct military conflict, rather it was a war fought with words, propaganda, economic weapons, and diplomacy between the US and the USSR.
Bloc- a group of countries that work closely together, during Cold War period (1945-1991) based on similar ideology