How do you become a knight and a sir?

When you become a knight the title Sir is automatic.

You become a knight by being knighted by a monarch.

The ceremony of knighting can be long and complex but its culmination by the initiate knelling before his monarch, being taping of each shoulder by the sWord of the monarch who says something like

I hereby dub thee knight. Arise Sir _____.

The monarch is at this point sometimes amused to give the knight a new name.

Sir Lancelot was call 'The Strong'

Sir Robin """ 'The Brave'

Sir Galahad '''' 'The Chaste'

Don Quixote "" 'Knight of the Woeful Countenance.'