I have some level of basic electronics knowledge, but I am only just learning arduino and having a lot of fun. Quick question. If I am just playing around with simple things like "Attaching a led to a pin using a circuit board" do I need to turn off (unplug) the uno? It seems like I shouldn't have to, but I just don't know what I don't know 
Thanks!
I do the deed at my own risk.
It is not a good idea to change circuitry with the power on, but some people get away with it, for a while.
I do not turn off the power, but have paid the price a few times!
But any 'active' devices, I always turn the power off.
You don't have to, it depends on
Play the odds: Every wire or diode or resistor you add to the breadboard gives you two chances to push it into a wrong hole. Do yourself a favor and switch off the power so you can double or triple check that before risking a goof up! (I have to do this because of my poor eyesight.)
@gosua, your topic has been moved to a more suitable location on the forum. Introductory Tutorials is not for questions. Your welcome to write one once you have mastered your problem 
@gosua, your topic has been moved to a more suitable location on the forum. Introductory Tutorials is not for questions. Your welcome to write one once you have mastered your problem
Thanks, and sorry for posting in the wrong location, I think I misread the title of that section.
No worries.
Always disconnect your project from power before changing/adding component connections.
Always double check your wiring connections before powering up your project.
I don't recommend it, but I do change circuitry with power on.
Almost always such changes are only what a switch might eventually be inserted to handle.
When it goes badly, I blame the cat.
The probability of damages is proportional to the cost of the components, your current inventory of replacements and the time it will take a slow boat to arrive with new stock.
a7
Very smart that you do not blame the wife.
I do it almost all the time. Have not had any problems with it.
Reminds me when I was working in a local radio station back in the 80's. The radio station did not have much money and the sound mixer was home made by someone who did not know how to solder properly. During a live sending we noticed that there was noise on one of the microphones.
It was possible to open the mixer at the top, so I opened it and saw that there was a bad soldering on the mic input. I turned on the solder iron and fixed it while they was talking in the studio 
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