Can be used as a greeting instead of saying "hello".. or "hey". If someone says "enna" to you, it it customary to used the word "enna" at the start of every new sentance after the intial enna greeting.
Person A : "Enna"
Person B : "Enna"
Person A : "Enna wanna get a doner kebab"
Person B : "Enna..I cant be asked"
Person A : "Enna.. it's got good chilli sauce"
Person B : "Ok I'll see you there"