As a question word:
* Что? (Chto?) - This is the most common and general form of "what" used in questions.
As a relative pronoun:
* Что (Chto) - This is used to introduce a relative clause, similar to "that" or "which" in English.
As an interrogative pronoun:
* Какой? (Kakoy?) - This is used to ask about the quality or type of something, meaning "which" or "what kind of."
* Какая? (Kakaya?) - (feminine form of "Kakoy?")
* Какое? (Kakae?) - (neuter form of "Kakoy?")
* Какие? (Kakie?) - (plural form of "Kakoy?")
Here are some examples:
* Что ты делаешь? (Chto ty delaesh?) - What are you doing?
* Я не знаю, что делать. (Ya ne znayu, chto delat.) - I don't know what to do.
* Что ты хочешь? (Chto ty khochesh?) - What do you want?
* Какой твой любимый цвет? (Kakoy tvoy lyubimy tsvet?) - What is your favorite color?
* Какая у тебя машина? (Kakaya u tebya mashina?) - What kind of car do you have?
The choice of the correct word depends on the context and the specific meaning you want to convey.