Right, here's a short guide to understanding ALL of the symbols:
-Floor. This is represented by periods, commas, apostrophes, and sometimes pluses.
-Wall. This is represented by filled colour tiles.
-Creatures. These are represented by letters.
-Dwarfs. These are represented by smiley faces.
-Everything else. These are represented by using the letter L when you come across them.
FUCK SO COMPLEX RITE?
But if you're really having trouble adapting to it, you should play around in the RPG Adventure Mode first. It's a lot less complex!
And if you can't get started, it's your own fault for not checking out
a tutorial.
As for the steep learning curve after the basics, well, that's part of the fun really. The main focus of DwarfFortress is that you lose! A lot!
Now on the subject of graphic tilesets, well, it's really a matter of personal opinion. I prefer ASCII, because it leaves more to the imagination,
which is one of the things that makes DF so fun; also, many characters are used multiple times for different things, so tilesets can often screw things up.
I also use Stonesense because it allows you to see things in proper 3D - DF only shows one layer at a time - but because this computer is so flipping slow I only use it for screenshots.
The one thing I really do recommend using is DwarfTherapist. Assigning jobs is the one big thing that the DF interface does NOT do well, whereas DwarfTherapist makes it a breeze.
The other thing I will say is that the controls are very... hap-hazard. Sometimes you have to use letters/numpad, sometimes you have to use the arrow keys, sometimes you get to use the mouse! It's something you never really get used to...