Learn Turkish: Bir saat sonra mola verelim. - Let us take a break in an hour.

When sonra directly follows a length of time without any endings, it means "[time] later" or "in [time]". To say "after an hour", you usually need the "from" ending (the ablative case), making it bir saatten sonra. Here, bir saat sonra simply means the action will happen one hour from now.

Could I use the "in/at" suffix and say bir saatte to mean "in an hour"?

Not for this meaning. Saying bir saatte focuses on how long an action takes to complete (like "I finished the homework in an hour"). To say that an event will start after an hour has passed, you always use bir saat sonra.

The word verelim comes from vermek (to give). Why does the translation say "take" a break?

Even though almak means "to take" in most contexts, Turkish uses a different verb for taking a break. The set phrase is mola vermek (literally "to give a break").

How is the word verelim formed?

It is formed from the verb root ver- (give) and the suffix -elim. The -alım / -elim ending is used to say "let's" do something together. Because of vowel harmony with the "e" in ver-, we use -elim to make verelim (let's give / let's take).