Learn Danish: Bageriet sælger masser af brød og kager. - The bakery sells lots of bread and cakes.

The suffix -eri can be added to verbs or nouns to describe an ongoing activity, an abstract concept, or—as in this sentence—a place of business. Here, it attaches to en bager (a baker) to mean a bakery. Nouns ending in -eri are almost always neuter (et-words), which is why the definite article added to the end is -et, making it bageriet.

Why use masser af instead of mange or meget?

Masser af (literally masses of) is a highly common, natural way to say lots of or a lot of. Its biggest advantage is that it works with both uncountable mass nouns (like brød) and countable plural nouns (like kager). If you didn't use masser af, you would have to split the phrase up based on countability: meget brød og mange kager.

Is brød singular or plural in this sentence?

It functions best as an uncountable mass noun here (meaning bread in general), just like in English. However, even if the bakery were selling specific loaves of bread, the plural of et brød is also brød. Since it follows masser af, it is grammatically correct whether you interpret it as a mass noun or a plural.