Vannary, Sarah-Charlotte, April: days of the week.

To ask someone what day is today in spanish you say "¿Qué dia es hoy?"
If you want to say "it's" in spanish you say "Es",  before you say a day you say "Es jueves (Thursday)"
"Today" in Spanish is "hoy"
Day in Spanish is "dias"

Don't get mixed up with American ways of writing days of the week. *NOTE* - the days of the week en espanol are not capitalized.

lunes - Monday

martes - Tuesday,

miércole - Wednesday

jueves - Thursday

viernes - Friday

sábado - Saturday 

domingo - Sunday

When someone asked you, "¿Qué día es hoy?" (which means: What day is today?) you reply, "Es viernes" [It is Friday] 

For the calendar when someone ask you, "¿Qué día de la semana es el 5 de Octubre? you respond, "el martes"

Semana = week.

Real life Application: When someone is asking what is today or the days of the week.