Is there some way to confirm compatibility of parts?

I never built a PC before and my main concern is that I am going to order parts that won't work together. Is there a website where I can enter 2 products in and get an answer either "yes it works" or "no it doesn't work".

If not, how do you ensure that parts will work with one another?

I don't know of a website that provides what you want.

If you're going to build yourself a computer, you really need to educate yourself on computer parts. Reading more on this forum will help. plus check out the various Tom's articles. Read on these forums what other people are building to get an idea of what works.

Other basics:

CPU: know the brand (AMD vs Intel) and socket type.

Video Card: understand which types there are (mainly PCIe) and if you ever want to run two or more, whether to plan for SLI or Crossfire.

Motherboard: what CPU you want and video card you want will determine which one you get. All about making sure the chipset of the board supports the CPU and video card you want. The chipset on a board determines what features a board has and what processors, video cards, RAM, etc, are supported.

RAM: Which type (DDR2 or DDR3 and the speed) again depends on which CPU you're going for.

Hard drives: SATA II connections are the standard for now. There are SSD and the tradational HDD types now.

Power supply: make sure it has enough juice to power your video card selection and is certified to work with your CPU.

Case: pretty much personal perference.

There's more out there, but those are the basics to purchasing compatible parts.