You already know that A E I O U are vowels. You also know that vowels can be tricky, because they can have very different sounds in English.
There are long vowels and short vowels.
The long vowels are the name of the letter, as in the Alphabet Song.
The short vowels are how the letter sounds.
A - long as in play and short as in apple.
E - long as in eagle (vivó Benfica!) or short as in hen.
I - long as in ice-cream or short as in insect.
O - long as in no or short as in doll.
U – long as in flute or short as in bus.
Practice here: http://www.starfall.com/n/level-k/index/play.htm
Practice here: http://www.starfall.com/n/level-k/index/play.htm