You need external speakers or headphones to hear sound from your computer. This feature of the soundboard really depends on what type of computer you have. Older model computers only have an ISA bus slot, and most new models have PCI bus slots. The more bits the better. The trend is that ISA is totally out, and PCI is in, so even if you need to buy a PCI slot altogether for a PCI sound board, it'll prove to be well worth your money in the long run.
All sound cards have the ability of outputting numerous different tunes and tones.
But it's how many of those sounds the card is able of outputting at the same time that makes the difference in the quality of a soundboard. Think of it as an orchestra. If you could hear 64 instruments playing at the same time rather than 16, you'd have a more complete acoustic experience. Current soundboards can carry as many as 512 simultaneous voices. Average soundboards should give you about 64.