How do I say "What I am doing"?
Firts of all, how do I ask "What are you doing?" and How do I answer that question. I'm doing homework, I'm watching TV, I'm playing videogames, etc...
"What are you doing" would be: （あなたは）何をしていますか。
And answer to it would be:
（私は）宿題をしています。 I'm doing homework.
（私は）テレビを見ています。I'm watching TV.
（私は）ゲームをしています。I'm playing games.
So generally, in the answer to this question you need: noun + 「を」 particle (it marks direct object) + verb with て-form (it's like "present progressive" in English).
何 ＝ なに
私 ＝ わたし
宿題 ＝ しゅくだい
見て ＝ みて
Did you not mean 何をしていますか for the question, the same as how you wrote it for the answer?
I would like to add, that using あなた (you) is rude under most circumstances. It's much better to use the person's name instead, or to omit it if the topic is clear from the context.