Im not very tall.You are ... than me.

Ты говоришь: "Я не очень высокий. Ты ... чем я."

In this sentence, you would use the comparative form of the adjective "higher" which in Russian is "выше." So, the complete sentence would be: "Ты ... выше, чем я."

I hope this explanation helps! If you have any more questions or need further clarification, feel free to ask.