I wrote a letter.
Watashi wa tegami o kaita.
I; me; private affairs; personal matter; secrecy; selfishness
topic marker particle; indicates contrast with another option (stated or unstated); adds emphasis
indicates direct object of action; indicates subject of causative expression; indicates an area traversed; indicates time (period) over which action takes place; indicates point of departure or separation of action; indicates object of desire, like, hate, etc.
to write; to compose; to pen; to draw; to paint