The days of the week
Les jours de la semaine

lundi – Monday
mardi – Tuesday
mercredi – Wednesday
jeudi – Thursday
vendredi – Friday

samedi – Saturday
dimanche – Sunday

If you want to say on Monday, on Tuesday, you just have to use the names of the days without any preposition:

lundi – on Monday
mardi – on Tuesday
and so on.

The days of the week are all masculine. If you want to express repetition (every Monday or on Mondays) use the definite article le before the names of the days:

le lundi – every Monday / on Mondays
le vendredi – every Friday / on Fridays

Next and last:

lundi dernier – last Monday
mardi prochain – next Tuesday

Some other words:

le jour – day
la semaine – week
le week-end – weekend
le jour ouvrable – working day
le jour de repos – holiday, a day off

aujourd’hui – today
hier – yesterday
demain – tomorrow
avant hier – the day before yesterday
après demain – the day after tomorrow

cette semaine – this week