Uses of さあ、まあ and なんか


I understand meaning and uses of あの、えと。 But I get confused when people use
さあ、まあ and なんか frequently while talking.




If I get your question right,

**さあ** Can mean :

>   * Who knows / I don't know
>   * Ok now/ there we go
>

And perhaps a few more, depending on the intonation.  
Example:

> Aさん:この人は誰？Bさん：さあね～。  
>  Mr. A : Who is that? Mr. B : Who knows.

**まあ** Can mean :

>   * Now now(mother reassuring kid)
>   * Sort of, kinda.
>   * oh, my!(Usually used by baasan)
>

And perhaps a few more, depending on the intonation.  
Example:

> Aさん:うまくいった？Bさん：まあね～。  
>  Mr. A : Did it go well? Mr. B : Kinda.

As for naka, perhaps you meant nanka. It is hard to explain, but can be used
to mean things like **you know** or **sort of**.  
Example:

> Aさん:どうしたの？Bさん：なんかさ～、今朝から具合が悪いんだよ。  
>  Mr. A : What's wrong? Mr. B : You know, I kinda don't feel good since this
> morning.

