How do I know what kind of video card I need for my pc?

I've bought two different cards, RADEON 4550 and ASUS AH3450 and neither of these cards fit on my motherboard. The RADEON would have because it is a pci express connection but when I try to connect it to the motherboard the out ports are on the inside of the tower....|||If you have a pci express connection, than the RADEON should connect to your motherboard. Are you sure you are connecting it right? All PCIe cards should fit into a motherboard with a PCIe slot.



I'll put a website in the source that is helpful for choosing a video card.