Listen, A and AN are same, THE is different.

Use THE in two cases,

1. when you are specific about any object.

suppose, I have a pen in my hand and that is the pen you want. so, you want the pen specifically. say, Give me the pen.

2. use THE when you want to indicate the complete race.

Every mango in the world of every species is sweet, correct? So, say. The mango is a sweet fruit.

Use A/An when

1.you talk about one piece/unit off something.

suppose, you just need a pen to write, any pen will do. So, say, give me a pen.

Want to buy 1 hamburger from the seller. say, give me a hamburger.

also

2. When you point to one object of any race.

Point your finger in the zoo and say, that is a tiger. (There are many tigers in the world and that is one of the tigers, correct?)

Use AN just like A when the name of the object starts with a vowel (a,e,i,o,u)

So, in the zoo again, point your finger and say, That is an(not a) elephant.

Hope this helps.

Troubles in english for me.

I often make mistakes when  I  using "the,a,an" in my english. I do not understand enough how to use it. If somebody can explain for me about how to use it, I will be pleasure pleased