You will need 2 flex slots for Healbane and Mystic Vulnerability You should first hit a left click to proc Soul Shredder Bullets that will also enable Mystic Vulnerability because you have Mystic Shot Then combo 2+3+1
This is a Yamato Build that's focused on your Power Slash ability to one shot. In early game just farm and poke your enemy to death. In lategame once you have refresher you can go all in 1v11 with double ult. Yamato is the character that requires the most skill and game knowledge in the game so it's not the best hero for new players.