A Sunday is not specific which Sunday On Sunday it’s specific

Hy Anya *On Sunday is when you refer to a specific sunday/this Sunday or maybe a past Sunday. E.g. I want to visit you on Sunday. Or I spoke to mom on Sunday. *On a Sunday is when you refer to any Sunday. E.g. I will visit you on a Sunday *On Sundays is when you refer to all Sundays E.g. I go to church on Sundays or I take the trash out on Sundays. Hope I make sense, and you understand.