ROMS

Generally speaking custom roms fall into 2 camps: modded stock roms, which are modified versions of the phones original software; and original roms which tend to be built from scratch for a number of models and tend to be based around AOSP(Android Open Source Project), basically barebone android without any manufacturer additions. Both have benefits and pitfalls. Modded stock roms are not hugely different from what you already have; they can be faster, more customisable, and generally less bloated than stock but at the same time they are changing something that the OEM has worked on for probably over a year, and what may seem to be an improvement in a devs eyes may not be to your taste. The speed can come at the cost of smoothness, stability, or battery life and possibly all three. Original roms such as CyanogenMod, AOKP, Omni, MIUI etc are designes normally from the AOSP source, not the manufacturers rom, so they will have the latest available version for your phone and have no carrier/manufacturer bloatware but also no original firmware, which means generally that apps designed specifically for your phone (camera, music, and so on) will not work. Plus once again, what some people define as better may not be your cup of tea.
I'm not familiar with Samsung devices, and generally all phones have slightly different versions of the process, but before you do anything you should root your phone, flash a custom recovery and make a nandroid backup so that you have your original set up available to restore; also back up your app data using Titanium backup or something similar. The reason for this is, when you flash a rom it will overwrite your current firmware and you'll probably be required to wipe user data too.
This is just a very rough guide, the best idea is to read the rom development thread to find out if there are any potential problems. Good luck anyway.

— modified on Apr 5, 2014, 7:37:08 PM

Yes, there's a free version which does most things. There are a few others which do something similar so check them out. A nandroid backs up your app data too but it's trickier, and sometimes impossible, to transfer it to another rom.
Once again good luck, don't hesitate to ask questions if you have any. Have a good weekend yourself.

No, it's actually NANDroid where NAND is the flash memory. It backs up a system image which can be restored and both processes require a custom recovery (CWM/TWRP) to be present. Basically, before you fish any rom or mod you should backup your current rom so that if anything goes wrong you have the option to restore your previous setup. Before anything you'll probably need to unlock your bootloader, root your phone, set up ADB on your PC/laptop, and familiarise yourself with the processes.
Like I said I'm not familiar with using or modding Samsung devices, so before starting to flash anything you should read up on it, and probably the best place is XDA. There are forums for almost all android devices, covering everything from the very basic to the extremely complicated. Obviously there are knowledgeable people here on AndroidPIT but XDA is more focused on android development. Feel free to ask here, of course.

ADB is something you would need to set up on your PC. It's basically a command-line editor to link with your android device(s) and a necessity for rooted phones. It's part of the android SDK (software development kit) and used to be pretty time consuming to find and install, but there are a few simple options now such as Koush's universal ADB driver, or even simpler is this ADB installer from xda. You'll also get fastboot which is required for flashing a boot.img(custom kernel) or other services such as unlocking your bootloader. Give this xda thread a thorough read before you do anything, as all devices differ; I only know Sony/HTC /Nexus methods and the above info is a generalisation of the procedures.

— modified on Apr 6, 2014, 7:16:32 PM

No problem. To be honest custom roms don't make a huge difference any more, more often than not you end up with poorer battery life and an unstable phone. I've been doing it for over 4 years but since dual core/krait cores the difference is minimal as most phones now can handle the stock bloatware without slowing down. Take your time reading the forums, there is a lot of knowledge that can be gleaned from questions and their replies. Enjoy the rest of your weekend anyway Randall, and always feel free to ask any questions.

Hey Randall, @Sinkster seems to have sorted you out pretty well on the basics.

Here's an article we posted recently about the best KitKat ROMs for the S3.

There's other more obvious and popular ones (like Sinkster mentioned) but these are some more interesting ones you might not have come across yet.

Search AndroidPIT for infographics too and you'll get a bunch of custom ROM articles twith infographic GIFs of their various features. Nice viewing if you want to get a quick overview of the major ROMs.