What sound does this make?
In my Arabic lesson, I came across the accent thing ْ, as seen in the word مَسْك
This word in the audio sounds like "mask," but even without the little circle accent thing on top, it would sound like mask.
I do not hear any change in pronunciation from adding this thing to the word. What does it mean? What does it contribute to the word, and what does it sound like?
The circle above a letter indicates that there isn't any vowel after the letter. The stroke above the letter indicates a short "a" sound, while below a letter it indicates a short "i" sound. Short vowel sounds aren't marked in everyday Arabic - you are just expected to know what they are. However, in learners courses (and some other contexts) they are marked. So whether the circle or the stroke is present or not doesn't affect the pronunciation, it just helps us beginners know what the pronunciation is.