Question

Question: when did Muhammad began preaching/ teaching Islam ​

Answer 1

according to Wikipedia, in 613 Muhammad started preaching these revelations publicly. proclaiming that God is one that complete submission to God is the right way of life and that he was a profit in messenger of God ,similar to the other profits in Islam

Answer 2

I think it was in the fourth year of Muhammad's prophethood, around 613, he was told by God to do his duty as a prophet and spread God's word.