Spanish has no word for "on" with a day: el lunes means "on Monday" and los lunes means "on Mondays". Months take en, and a date is simply the number - el cinco de mayo. Days and months are written in lower case.
Examples
- Tengo clase el miércoles.
- I have class on Wednesday.
- Los sábados no trabajo.
- On Saturdays I don't work.
- Mi cumpleaños es el ocho de abril.
- My birthday is on the eighth of April.
The mistake to avoid
Don't translate "on" as en with a day - "en lunes" is wrong; it is el lunes.
Where this fits in
Numbers, days, time, Spanish A1: Count, talk about days and months, give the time, and handle numbers in real situations.