I have something to ask.

What does this expression mean on turkish?And when can I use it?

-Kendine gel

Does it mean: come to yourself?

but doesn´t gel mean COME....? and git - go...?

I think the literal translation is come to yourself, but it´s meaning is like ´come to your senses´,or ´see some sense´ kind of thing. But I´m not sure, someone will help more I´m sure.

Come by yourself ? 

No. Arica is correct here it means come to you senses ,see the light

 kendine gel=behave yourself

you can uýse it when s.one tells you s.thing but he has no right to tell you that or it is none of his business to tell you this or that ...

or when s.one uses a humiliating word then you can tell him "kendine gel"and mind your own business .