So I want to play sound a(n) .mp3 file off of a(n) SD card and display tags on the 20x4 BLUE LCD I have to make the SD reader myself, it is for a competition and I'm probably going to be the only one using an Arduino for micro-processing, back on topic though I need some help connecting this SD card slot I have no idea what type it is I will get pictures of it when I see it tomorrow. I simply am soldering wires to every pin out on the reader itself it's just a simple 8pin SD card slot.
I'm needing some help though, I have to program this and connect all the pins to my LCD and my SD card I have no idea how to connect either to the Arduino itself, I came to you looking for help in this field, if anyone even has experience hooking up an SD card reader and some sample code I would be so excited. I hope someone can help me, I sure in the hell can't help myself. I'll be on here for another hour tonight and early in the morning from school to post pictures and read all the helpful tips you guys have to say. Thanks for reading this whole thing through. 
Also, if I win I will love YOU guys forever.
Adafruit has a "waveshield" that has SD card and D-A converter plus audio amp, designed to play .wav files from the SD... Schematics, board, and code all open source so you can look at it as an example for your own stuff...
I don't think an arduino cpu is capable of decoding MP3 files, BTW. Not without hardware assistance or VERY clever code.
Hmmm, Well then .wav files would be a little easier. It's just I can't use the shiled or I would.