"Ma grand-mère priait à l'église tous les matins."

Translation: My grandmother used to pray at the church every morning.

[luluhunter]

Why do we have to use the, why not just, used to pray at church

[Hwin_74]

most times you need a 'determiner' before french nouns. Articles are determiners. Some prepositions like 'en' /sans are determiners. Quantitative phrases/words are determiners... like vingt (twenty apples) beaucoup de pommes (a lot of apples). But prepositions of position/place like 'a' and dans' and 'a cote de' etc need the determiner (USUALLY one of the articles) before the noun which follows.
I think you are being thrown by having to translate phrases like "we are at church" in english to literally 'we are AT THE church' in french. But remember you can say "i eat apples' in english but MUST say literally 'i eat (some/the/two/...essentially a determminer) apples in FRENCH!

[JohnIzebhi1]

Can we also write "used to pray every morning at the church"

[Lucien660983]

It's correct, but there's no reason to change the word order here, if we want the translation to be literal, in my opinion.

[Antti546484]

"My grandmother used to pray every morning at the church" was accepted.