"I write."

escribo means "I write", whereas escribe means "he/she writes" or "you (formal) write".

That would be something like "I am I write".

You use soy when talking about something that you are. For example, you could say Yo soy muy inteligente. That means "I am very intelligent". If you were to say Yo soy escribo, you would be saying "I am I write".