Conversation so far:
How did he start his teachings?
Namdev's songs were composed to be melodious and carry a spiritual message.
They built on one among the many ancient Indian traditions for making music and singing.
What were the Bhajans?
Namdev composed bhajans, that is songs meant to be sung to music.
A Bhajan literally means "a thing enjoyed or shared.

Question: Who did he teach the Bhajans to?
Self-contained rewrite: Who did Namdev teach the Bhajans to?