What does it mean?

Okay I get an email when someone moves which is quite nice, but in
the email there is always something like this

FEN value before move:
rnbqkbnr/ppp2ppp/4p3/3p4/3P4/2P5/PP2PPPP/RNBQKBNR w QKqk d6
0 3

And I have no idea what it means. Where on the site is this
explained?

Also I would like to add to the requests to be able to send messages
when it is not your turn. Often I mean to send a message but then
get caught up in moving the pieces and forget about it until I hit the
moove button and then it is too late.

For an explanation click on the red question mark with "help me!"
below it (top(ish) right of your screen). Then click on "pop up help
files", then "FAQ", then number 8 "What is a FEN".

Mark

Ahh yes. Thanks.