Pretty good short explanation in the Wikipedia article. Pretty easy to get at least the main board set up correct without needing to look up anything. I always have to look up what the last fields are if I'm creating one from an OTB position.
http://en.wikipedia.org/wiki/Forsyth%E2%80%93Edwards_Notation
Was fen a grandmaster
According to the wiki article, the F is from David Forsyth (1854–1909) and the E from Steven J. Edwards who came up with the PGN specification and extended Forsyth Notation to be more usable by computers.
Forsyth won the New Zealand Championship in 1901 but I have no idea what his overall chess strength was. From some Google searching the book "The Chess Bouquet" states he was strong player and "he won a majority of games against the strongest and most experienced players in Scotland, and for a time seemed first favourite for the championship."
There are three Steven Edwards in the USCF database, though I don't know if any of them are him but I'm pretty comfortable in saying he isn't a GM.
Could you please give an example of how to create a FEN string? I tried creating a diagram but i keep getting a string parse error. Thanks