completely new to Arduino. I don't have any units yet. wanting to set up a bank of randomly blinking lights in a 'bank' for a costume 'greeble'. can someone give me some guidance as to what board to use and how to program it? I am looking to have this ran by an external battery (possibly 12VDC). somewhere around 15-20 lights blinking completely randomly, can have more than one on at a time. if possible, when/if more than one is on at a time, can it be also random which 2 (or more) are lit at the same time?
How long must the battery last ?
How far apart are the LEDs ?
What LEDs ?
What wire is being used ?
8-10 hours for the battery, and rechargeable.
LED's would be relatively close - all of them within 2 inches by 4 inches.
no idea for what LED's
also same for what wire -- although I have some 22GA wire laying around
Thanks
edit = 22GA stranded, in case it makes any difference
@quemeese, your topic has been moved to a more suitable location on the forum. Introductory Tutorials is for tutorials that e.g. you write. Feel free to write a tutorial once you have mastered your problem.
yea, I'm pretty much clueless
You need to choose the LEDs first (type and number) so that you can estimate the average current that will be drawn from the battery. Then, with the desired time between charges, you can calculate the require battery capacity in mAh (milliamp hours).
Well, first suggestion; definitely not a UNO. 
A UNO is particularly difficult to connect up, and all the more so for a costume where movement is involved and secure connections are required.
The Nano will be the most practical in many respects - I will leave it to you whether you purchase a genuine one from Arduino.cc to support the project, or a cheap Chinese "clone" which will generally be just as reliable.
Of course you need to be able to solder, presumably you already can?
As @groundFungus mentions, what LEDs did you have in mind? You presumably do not need any brighter than the common variety which operate at 20 mA per colour as it will presumably not be worn in daylight. OK?
And yes, what colour? An option is the "NeoPixel" or WS2812 LEDs which are completely colour selectable to the extent of any shade. An advantage is that you wire them (or purchase them already assembled) in a chain which connects only to one Arduino control pin, simplifying the wiring.
Now LEDs operate at a few Volts and the Arduino at 5 V, so a 12 V battery would require a switchmode "buck" converter to convert to the required 5 V. A USB "Phone charger" or a 4 cell "AA" NiMH rechargeable battery pack would probably be more appropriate.
I’d suggest you start simple, playing with the examples included with the IDE - blink a single LED.
Then look into sketching out how it will be wired together.
As said above you need to identify what you’re working with before starting.
You WILL make some mistakes, so it’s better to understand why they’re mistakes before running into a brick wall.
It may seem simple, but blinking a single LED is simple… blinking two LEDS is easy… blinking multiple LEDS is a bit harder, and blinking multiplexed LEDS or smart LEDS is quite complex under the covers.
Read up on using millis() for the timing instead of delay - as you get better, everything will become clearer!
how do I decide what LED's to use?
told you I was a complete beginner........
Can you give us a better description of what you want to do with the LEDs?
What size? There are sizes from tiny surface mount, 3mm, 5mm, 10mm discrete LEDs and there are LED strips.
Do you want single color LEDs, RGB LEDs, or RGBW LEDs?
like in an old scifi movie or TV series, a working computer would be shown as a wall of randomly blinking lights - but on a much smaller scale. about 2"x4" with maybe 20 lights, max. probably 5mm and multiple colors. LED strip sounds like the whole strip would light up all at once and don't want that.
also, I'm not very good at it, but I can solder.
For sewing, costumes, etc., the Arduino Lilypad line is usually used, with its range of peripheral sensors, buttons, LEDs, etc. Even sewing thread is conductive.
Browse that range of products before you decide.
note: no sewing will be involved here -- does that change anything in whether to look at the Lilypad?
And how do you plan to glue the arduino or the leds to the costume?
and how to lift the driving cables?
for the Arduino, probably make a slot to fit it into, with perhaps a strap to secure it.
hadn't actually thought of gluing the LED's, just thought I would make holes in some EVA foam and push them through.
Everything is possible of course. But the Lilypad family of products was invented for sewing. All its terminals are not designed to be soldered, they are designed to be sewn with a conductive thread and make a kind of pcb on the dress or costume.
Take a look before you decide
yep, won't be going with Lilypad.......
A strip like the WS2812B RGB LED strip has individually addressable RGB LEDs. One wire from the Arduino can control hundreds of LEDs.
The strips can, easily, be cut into smaller strips or individual pixels and wired how ever you desire.
The strips come in different densities (pixels per meter), too.
well then you may be interested in this type of led that does not form a strip.
can this be trimmed to size?