Used as a noun or time adverbial for the day of the week. It can take particles such as は and に, or appear at the start of a sentence as a time expression.
月曜日は燃えるごみの日です。
Monday is burnable trash day.
次の月曜日に会いましょう。
Let's meet next Monday.
月曜日、朝一番に電話します。
I'll call first thing Monday morning.
The meeting is on Monday.
I go to school on Monday.
I work from Monday to Friday.
I put out the trash every Monday.