Wow! You have a cheek taking money from students as "a professional English teacher" when you don't know the difference between the definite and indefinite article!
٢ نوفمبر ٢٠١٨
1
3
3
You are advertising yourself as a professional English teacher with English as your native language and you don't know even the basics of the English language?
٢ نوفمبر ٢٠١٨
1
3
1
'a' is an indefinite article so it means 'a gym' is one of many possible gyms it is not said which gym it could be.
'the' is a definite article it means 'the gym' is a specific gym probably the only known gym in town. The hearer usually understands which gym.
٢ نوفمبر ٢٠١٨
4
1
1
'the gym' is like 'the post office' or 'the bank' - any of them suffice for the purpose, and no one normally asks 'which one'.
'a gym' is like 'a restaurant' - a situation in which a choice is made between alternatives.
:)