Motherboard selection help, please?

I've always liked AMD motherboards but honestly if you're focusing on budget/mainstream then really any brand of board will do, just pick out which features you want and you're set. Just make sure you don't judge a budget board too harshly against the big bad performance overclocking boards, it doesn't appear that you need lots of PCI-E slots for running multiple video cards or overclocking your system much. Personally in your case I like the looks of ASUS M5A97. If motherboard layouts confuse you then there are a slew of youtube vids out there going over all the different types of components you will see on a motherboard, you may also go to various sites like Newegg or manufacturer websites and look at pictures of the board which usually will point out all of the main components on the board. The user manual that comes with the motherboard will also show you all of the connectors.

Chipsets are what allow all of the components on a motherboard to talk to one another (CPU/memory/video/peripherals). As new advances and capabilities are designed new chipsets are released and motherboard manufacturers will then build their boards around the new chipsets. Each time a new chipset comes out (at least currently with AMD) they will provide several different options of the same chipset which have different performance. Think of trim levels on cars, you may have an Accord DX with manual windows and no AC and then an Accord EX with all the bells and whistles. Currently AMD's highest chipset for AM3+ sockets (socket is the design of where the CPU attaches to the motherboard) is the 990FX which you'll find on more expensive boards, you then have the 990X, 970, 880 and 760 being the lowest on inexpensive boards. Personally for what you're going for I'd pick something more in the middle (like the Asus board above).

POST stands for Power On Self Test, when you turn on your computer your system will run through POST to make sure all of the components and systems are functioning correctly before attempting to load the operating system (windows). if POST is successful then great your OS loads, if not due to a BIOS setting issue, you will be forced to enter your BIOS, if it is due to hardware failure then you will most likely hear loud beepings/sirens. Modern boards will even have LED indicator lights and even error codes to refer to so you know exactly what is causing the problem. I dusted off some old hardware the other day to test it and I forgot to plug in the auxiliary PCI-E power cable into the video card, when I turned on the computer it would not post and only gave me a very loud steady siren. Doesn't necessarily hurt anything, it just lets you know that you suck at life 7 times out of 10 a conversation about POST'ing usually involves overclocking, the higher an overclocker pushes their system the sooner they have stability issues. Sometimes an unstable overclock will result in a Windows crash, other times you cannot even POST. If not overclocking then usually people talking bout POSTing are trying to troubleshoot what part of their system is causing POST failure, maybe the memory is bad or something isn't seated correctly.

Regarding parts, everything looks ok however depending on how many devices you'll have powered on or even a bit of light overclocking you may consider a bit bigger PSU than 500w, but really I think you'll be ok. HD looks good, the Barracuda name doesn't really make the drive any more special than any other 7200RPM harddrive out there, you're really good going with whatever brand is the cheapest with the highest user rating. Everything is all about the SSD's now (solid state drives, instead of spinning platters you just have memory chips) so really performance wise a lot of the standard hard drives are the same. Also I'm not sure how hot the 6300's get but you could probably save a few bucks going with a nice air cooler vs the water cooler in a box.

Cables wise things have come a long way since the computer you have now. Generally PSU's have a 24pin main power connector for the motherboard, a 4 pin or 8 pin auxiliary CPU power connector on the motherboard, a 6pin PCI-E power connector for the video card, some 4pin molex connectors to power things like fans, then SATA power connectors to power your SATA drives (harddrives, opitical drives, SSD drives). Back in the day drives used 40/80 pin IDE ribbon cables but most everything is SATA now which is one single low profile cable, it helps a lot with the mess. Power supplies have come far too, a lot of the enthusiast brands now pre sleeve the cables to clean things up and also have modular power supplies which allow you to disconnect power cables that you don't use from the power supply itself.