Tea culture exists around the world in many different forms. My experiences with Russian tea culture have helped me to feel more welcomed and at home in a new city.
Whenever you enter a home or living space in Russia, you are immediately offered tea. However, "tea" usually does not just include drinking tea. Instead, it is often a huge spread of cookies, cake and candy. It also often leads to a full meal, with the simple purpose of welcoming you into a home. This tradition takes place not only in homes but also in work spaces. Whenever I walk into the Russian department where I take classes or the English department where I teach, I am immediately offered tea. The departments have teacups and mugs ready for everyone's use, and more often than not, there's a selection of cookies or candy to choose from.
As in many cultures, hospitality and friendship are really important pieces of Russian culture. Offering tea and food is a way to make people feel comfortable and at home.
I think tea originally gained popularity because it is warm and soothing when it is very cold outside. Since winters in Russia are usually cold and blustery, welcoming guests with tea so that they could warm up became an important tradition.