Perhaps the main point to know about the physical geography of Russia is that it is an enormous country. If you count the islands in the Arctic, Russia is about 4500 kilometers (2800 miles) from north to south and 9000 km (5600 miles) from east to west. It is so big that it encompasses 11 time zones.
Russia is divided into an eastern part that is in Europe and a western part that is in Asia. The western part is typically called Siberia. The Ural Mountains run north to south and serve as the boundary between European Russia and Siberia.
Russia has many rivers. The rivers in Russia mainly run north to south. The majority of the water carried in those rivers flows into the Arctic Ocean. The largest river in Russia, the Volga, does not even flow into the ocean. Instead, it flows into the landlocked Caspian Sea. One of the rivers in Siberia, the Yenisei, carries more water than the Mississippi and another, the Lena, carries about the same amount as the Mississippi.
Russia has three main biomes and two other major biomes. The three major biomes are taiga, deciduous forest, and steppe. The two other major biomes are desert and tundra.
There is, of course, much more to be said about the physical geography of Russia, but this is a basic summary of the main points to know.