Who, what, where, when, why and how. They are commonly used with questions and always have a written accent.
'Qué' is used instead of 'cuál before a noun. It asks about a description, explanation or definition.
'Quién' refers to people.
'Cuál' is used before the verb 'ser' except when asking for a definition or explanation. 'Cuál' asks about a choice or selection.
'Cuándo' indicates time.
'Cuánto' indicates quantity or intensity.
'Cómo' indicates ways and means.
'Por Qué' asks for a reason or explanation of why.
'Para qué' asks why, or for what purpose, is something being done.
'Dónde' indicates a place or location.