Adverbs of frequency are words that tell us how regularly something happens. 
We can imagine these words on a scale from zero, meaning never, to 100%, meaning always.

0% ——– ——— ——— ——— ——— 50% ——— ——— ——— –——- –——- 100%
never, rarely, seldom, sometimes, occasionally, often, usually, almost always, always

Positive: subject + adverb of frequency + verb
Negative: subject + do/does + not + adverb of frequency + verb
Question: Do/Does + subject + adverb of frequency + verb?

• Always means 100% of the time.
  She always eats breakfast in the morning.

   

• Usually and often are synonyms that both mean most of the time.
  He usually goes to bed early.
  They often visit their friends at the weekends.

   

• Sometimes and occasionally are synonyms that mean a small number of times.
  I sometimes go to the cinema on Fridays.
  They occasionally treat themselves to a Chinese takeaway.

   

• Rarely and seldom both mean something that happens very few times.
  He rarely sees his old school friends.
  Kristina, the English teacher, seldom shouted.

   

• Never means 0% of the time; something that doesn’t happen at all.
  She never forgets her daughter’s birthday.