Catalan has no word for "on" with a day: el dilluns means "on Monday", and els dilluns means "on Mondays". Months take a l' or el, and a date is el plus the plain number. Days and months are lower case.
Examples
- Tinc classe el dimecres.
- I have class on Wednesday.
- Els dissabtes no treballo.
- On Saturdays I don't work.
- El meu aniversari és el vuit d'abril.
- My birthday is on the eighth of April.
The mistake to avoid
Do not translate "on" with en before a day - the article does that job.
Where this fits in
Numbers, days, time, Catalan A1: Count, talk about days and months, give the time, and handle numbers in real situations.