This is pretty rough and basic. This has served its purpose for me, but there might be an easier way to do it.
ADB is a very handy tool when interfacing with your phone. Fastboot I don't use with my S3, but I do use it with my Xoom and with Nexus 7. Also, when I was unlocking my Atrix 4G, it seemed like every command was executed through fastboot, there were not easy to use tools at the time to unlock the bootloader and install customer recoveries.
Here is a quick overview of basic commands for ADB and Fastboot:
What is ADB?
Here is how I install both of them on my computer. If anyone has an easier way, or something less confusing, or a more useful use of the Android SDK as it applies to most users, by all means, throw in some input. There are tutorials all over the internet on how to install them and use them. I find this way the easiest for me.
You will need an archiving program such WinRAR.
WinRAR archiver, a powerful tool to process RAR and ZIP files
Download it and install it. You can use WinZip but that is like so 10 years ago!
Now go to your root drive. (For Windows users this will be your C: drive. Mac and Linux users, I have no idea. I am trying to get some VM's installed to learn though!!)
Make a folder in your root drive. Try to keep it short. I usually use dev (all lowercase). It becomes difficult to type out long strains of directories
Head over to developer.android.com and download the Android SDK. The link is on the main page, labeled: Get the SDK. Click it!
On the right hand side of the page, click "Download the SDK".
Make sure you agree with the terms and select your computer's OS capability and download the SDK ADT Bundle for Windows. If you are running Linux or Mac OS, there are separate links for you towards the bottom labled: Download for Other Platforms.
Once the bundle has downloaded, navigate to the folder it downloded in to. Right click on it and "extract to adt-bundle-windows-x86_64-20130219".
Open the folder "adt-bundle-windows-x86_64-20130219" and you will see another folder with the same name. Open that folder as well. Open the "platform-tools" folder. Open the "sdk" folder. This has your adb.exe and fastboot.exe.
Because I am ignorant and do not know any better, I take all the contents of the folder and copy them. From there, I throw them in my dev folder on my C: drive.
Next, we have to open the Command Prompt. In Windows 7, you can simply hit Start and do a search for CMD.exe. Once you find it, click on it and open it.
In order to execute adb or fastboot commands, your command prompt has to be pointed to the proper directory.
To do this, type as follows:
C:\Users\yourusername> cd C:\dev and hit enter.
Your prompt should now be set to C:\dev
Now you can execute adb and fastboot commands.
Plug your phone in to your computer and let your computer recognize it.
Type "adb devices" without the quotes and you should see:
adb server is out of date. killing...
* daemon started successfully *
List of devices attached
ADB is working properly and it sees your device.
Now that you have ADB running you can do things like back up your IMEI, and in the event a bad flash is made, you can recover it!