Learn Swedish: Allt i frysen började tina. - Everything in the freezer started to thaw.

Allt translates to "everything" when referring to things in general, treating the collective group as a neuter concept. You would use Alla to mean "everyone" or when referring to specific countable plural nouns, like alla matvaror (all the groceries).

Why is there no att (to) before tina? The English translation says "started to thaw".

In Swedish, the verb börja (start/begin) is very often followed directly by an infinitive without att. This contrasts with phrases like var tvungen att (had to) from your current lesson, which strictly require att before the next verb. While började att tina is also grammatically correct, dropping the att is much more common and sounds more natural.

Why does the sentence use frysen instead of frys?

Frysen is the definite form, meaning "the freezer". Just like in English, we use the definite form here because we are talking about a specific freezer in the context of a home, rather than just any freezer.

Could I use smälta (melt) instead of tina (thaw) in this context?