The motherboard is where it all comes together for a PC. The motherboard connects everything together in your computer. The CPU may be the heart of your computer. The motherboard is the skeleton on which everything connects to and comes from. All your ports, and connectors are on the motherboard. What motherboard you pick out will determine what other components you buy, and for that reason, I recommend you pick out the motherboard first.
You have to be very careful with the specs on a motherboard to get the motherboard you want. Let's go through what to look for and what the spec is telling you.
The motherboard has a socket for your computer chip. Since at this writing I recommend the Intel Core 2 Duo chip set, this will mean that your motherboard must have an LGA 775 socket. There are other sockets out there, like the LGA 1366 for example, so search for LGA 775 motherboards, if you want the Intel Core 2 Duo chip set.
Next memory, memory needs 240 pin slots, some motherboards come with two slots and some with four slots. Since memory comes in matching card pairs, and the current memory cards max out at 4 Gb per card, the most memory you can have on a two slot motherboard is 8 Gb's. You may think that you want four slots, in which case you will be told the motherboard supports 16 Gb of memory. This is misleading. In order to use more than 4 Gb's of memory you need to use a 64-bit CPU, which we are not using. The advantage of the four slots is you can chip away, literally, and gradually add memory to your system in the future. Come on, this is hooey, too. Do yourself a performance favor and maximize your memory right from the start. And that, with the Core 2 Duo, is 4Gb. You can order it with two 2Gb cards, or four 1Gb cards. With the former you'll need two memory slots on your motherboard, with the later you'll need four slots.
While we're talking memory, motherboards are designed to use a particular type of memory and memory speed. There is DDR2 and DDR3 memory, and runs at various speeds. DDR3 is the latest technology. Currently there are not a lot of DDR3 motherboards made as technology catches up. It's ok to use DDR2. Try to get a memory speed number that is over 1066. This will mean your motherboard is a later model. No matter which memory you end up with DDR2 or DDR3 you must match the memory you buy to the motherboard type and speed of memory called for in the motherboard spec. They have to match.
Now to graphic cards, graphic cards connect using a PCI Express 2.0 x16 socket. All motherboards have one. You may want two slots, if in the future you want to expand to use two graphic cards. If your not a gamer, this shouldn't matter, however if you are a gamer, not only do you need two slots, but they need to be the proper distance apart so you'll look for motherboards that claim their SLI ready for NVIDIA boards. You'll also then need to look for graphic cards and power supplies that are SLI-Ready. For ATI graphic card users will look for the word "Crossfire." If you are ok with one graphic card, then a one slot PCI Express motheboard will be fine.
Since you will be buying a separate graphics card, you do not want a motherboard with an on-board video chipset. See my graphic card post for more explanation.
Next SATA connectors, Each of your hard drives will need to connect to the motherboard. Since you will be getting SATA hard drives, you'll need SATA connectors on the motherboard. Also the newer DVD drives use SATA connectors. I recommend you have a minimum of four SATA connectors on the motherboard.
You may, or may not, want to use RAID when hooking up your disk drives for safety. This is a entirely new topic, which I will address in another post. For example, to mirror your disk to another disk drive you will use RAID 1, which implies you will purchase two identical disk drives. Each RAID set up requires a different number of physical drives, and thus may require more than four SATA connectors and more power. Since we are building a basic computer, I will not recommend you use RAID at this time, so for now just ignore the RAID specs.
Audio - today's motherboards have sophisticated audio built into the motherboard. Bear in mind you will have to purchase a set of computer speakers or output your computer audio to your audio-in on your stereo receiver to hear anything. Look for something like Realtek 8 channel audio on the spec with 6 audio ports.
You want an Ethernet RJ45, better known as a LAN chipset. And as many USB 2.0 ports as possible. The latest keyboards and mice use USB connectors, then you may want to plug in a USB jump drive or back up disk. It should have a minimum of four USB 2.0 ports. Most boards have an IEEE 1394 interface, called firewire.
You want an ATX motherboard for your ATX computer case, unless you want to go for a small case and use a microATX board. Make sure your case fits an ATX board, most do.
You can purchase a motherboard for as little as $41 and as much as $269. How do you choose? There are a lot of motherboards out there. The most popular boards are made by Asus and Gigabyte. Some boards have a wireless lan built-in to the board, most don't. Most of the higher price boards are built for two graphic cards, you don't need that if your not going to buy two graphic cards.
Other than that, I would read the reviews, see what other users are saying about the board, is it reliable, how's the support, what kind of problems are others having. You get the idea.