Some students become very confused by two articles "a" and "an". Most times it is as easy as; a,e,i,o,u. If there is a vowel present in the noun you are generally told to use "an". However, there are exceptions. These exceptions are due to "sound-likes". Examples:

An Hour has the silent H... sounds like "our"
A University becomes a tongue twister if you would use "an"
A European has the "your" sound

Remember these are just examples.