So the Slavs are a branch of the Indo-European peoples.
They were living as different tribes in an area where is the today Ukraine. From where they come from? From India? From Siberia?
I think they came from the same place as all other Indo-European peoples came. The question is where and when they parted from other Indo-European peoples. The linguists who study Indo-European languages assert that there are two main branches of these languages: centum and satem languages. Centum-satem isogloss - Wikipedia, the free encyclopedia
This partition occurred approximately 4000 years B.C.
Here is a map of the сentum/satem languages distribution in 2000 B.C.:

Very approximate diachronic map showing the centum (blue) and satem (red) areals. The hypothetical area of origin of satemization according to the inventor of the idea, von Bradke, is shown in darker red, which happens also to be the range of the Sintashta/Abashevo/Srubna cultures. Whether the map is accurate in many of its other details depends on the time period considered.

Slavic languages are satem languages whether most languages of Western Europe are centum ones. When did the Proto-Slavic language parted from ancient Satem language I don't know.
Three additional historical questions:
1. When historically Slavs formed a common alphabet based on the Greek alphabet?
2. When they become Christians?
3. When the tsars came in to power? (I think there are two dynasties).
1. The Slavs don't have common alphabet. Most of the Eastern and South Slavic peoples use the Cyrilic alphabet but the Western and some of South Slavic peoples use the Latin alphabet.
2. Not all of Slavic people are Christians, but the majority is. The Western Slavs are mostly Catholic, although they earlier used to be Orthodox Christians, most of Eastern and South Slavic people are Orthodox Christians.
You probably want to read something about Saints Cyril and Methodius:
Saints Cyril and Methodius - Wikipedia, the free encyclopedia
3. The answer depends on what meaning you put into the word "tsar". The monarchs who ruled ancient Russian principalities used to call themselves "князь" (prince). The word "tsar" is probably the Slavic pronunciation of the Latin word "Caesar" which means a ruler of an Empire. So the first Russian Tsar was the monarch who proclaimed Russia to be an Empire, and Moscow to be The 3-rd Rome. It was Ivan IV the Terrible. All his predecessors were "Great Princes" (Великие Князья).