What was Lenin's "April Theses"?

Lenin's "April Theses" represented a radical change in the Bolsheviks' political strategy. Previously, it was widely accepted that the Bolsheviks should work within the system of liberal democracy established by the February Revolution of 1917. This was in keeping with orthodox Marxism which argued that a Communist revolution could only take place in a society where capitalism was fully developed. As that most certainly wasn't the case in Russia, most Communists felt that it was necessary for the capitalist system and its political institutions to develop further until the time was ripe for its overthrow.
The "April Theses" abruptly turned that way of thinking on its head. Among other things, Lenin now advocated non-cooperation with what he condemned as the "bourgeois" Provisional Government. The bourgeois revolution, the necessary preliminary to a proletarian revolution, had already taken place; now it was time to move on to the next stage. Instead of working with the system, the Bolsheviks were now committed to destroying it altogether.
To this end, Lenin set out in the "April Theses" a number of radical measures such as the nationalization of the Russian banking system, the abolition of the police, army, and bureaucracy, and the establishment of a republic based on the soviets, or workers' councils. Although many of these measures were never enacted, the radical nature of the "April Theses" provided the ideological underpinning for many of the Bolsheviks' policies after they seized power in October 1917.
https://www.britannica.com/event/April-Theses