The rule as a picture, 5 multiple-choice questions, 3 sentences to correct and a short writing task. Free to print and copy for your class or for self-study.
Want the explanation first? Read the A vs The lesson
Use a / an when the listener doesn't know which one you mean, or it doesn't matter: I talked to a manager. Use the when you both know exactly which one: I talked to the manager. (the one we both know about)
I talked to a manager.
I talked to the manager.
Write two sentences about your own life: one with A / An and one with The. Then explain the difference to a partner.
Answers will vary. Check that each sentence follows the rule on page 1, or paste them into Clarigram to have them checked.