Learn French: Le mardi, elle travaille à la maison.

In French, you use the singular article le before a day of the week to show that an action is a recurring habit. So, while le mardi literally translates to "the Tuesday," it means "every Tuesday" or "on Tuesdays".

Why isn't the word for Tuesday (mardi) capitalized here?

Unlike in English, days of the week and months are not capitalized in French unless they are the very first word of a sentence. Since Le is the first word here, mardi stays lowercase.

Doesn't maison mean "house"? Why is it used for "at home"?

Yes, maison means "house." However, the fixed phrase à la maison (literally "at the house") is the most common and standard way to say "at home" in French.

I sometimes mix up verb endings. Why does travaille end in just an "-e" here?

Travailler (to work) is a regular -er verb. When matching it with elle (she), the correct present tense ending is just -e. You would only use the -es ending (travailles) if the subject was tu (you).