It's not especially the fact that a wall socket is 230V (or 115V for whoever else) that kills you, it's that it operates AC at 50Hz. 230V at a maximum of 13A (30A if you just get two metal prongs, jam them into the socket and then touch them both) is more than enough to cross into the human body.
[Note here: I think the voltage is a constant 230V, the current [amps] goes down dependant on the resistance in the circuit, ie, your body.]
But the 50Hz going through your body causes your heart to fiblirate (ie try to beat 50 times per second, which it fails miserably at). That's why you can use a defiblirator (you know, those paddle things you seen in ER, etc.) to help a person that's had an electric shock from a wall socket.
Substations and the like can have 10k-250kV running through them, that just burns you to cinders.
[The way to think about current and voltage is like a pump pushing water through a pipe. The voltage is how hard the pump is pumping, and the current is how much water is actually flowing. Using the same pump to pump through a small pipe (high resistance) will mean less current flows through the pipe, whereas if there was a big pipe there would be more water flowing - more current - due to a lower resistance].
Does that cover it?