Since English isn't your first language, here's a tip for an/a usage:
Use "an" when the first letter of the next word is a vowel (e.g. an apple, an egg, an idiot, an orange, an umbrella)
Use "a" when the first letter of the next word is a consonant (e.g. a headache, a dog, a plane, a cow)
You should probably revise that, because the first letter doesn't matter, it's the first sound. e.g. I would not say a honest person, I would say an honest person. Because, although the first letter is an H*, the first sound is that of the O.
* an H is another example
