This is the 16th most frequent Russian word.
то
"То" means "that" or "it" in English, depending on context.
Conjunction:"то" used as a logical consequence marker.
Если бы я знал об этом раньше, то я бы поступил иначе.
If I had known about this earlier, then I would have acted differently.
Demonstrative pronoun:"то" referring to the subject of the following clause.
То, что он сказал, удивило меня.
What he said surprised me.
Conjunction:"то" paired with a condition to indicate a consequent action.