I use Gimp but I'm sure the instructions are pretty much the same for other photo manipulation software. Gimp is my choice because it's free and there are bits of it I can understand. If only I had more time to work with it, I'm sure I could do some pretty cool things. But I'm a confirmed amateur, and I'm deliberately avoiding any technical language here because I just don't understand it.
Anyway, here goes! Hope it's helpful.
Open your photo in Gimp - you perhaps want to make a copy to work on. Here's some tigers eye and carnelian earrrings looking a little grey and flat. What I'm showing you here is how to get a white background and make the image stand out but without distorting the colours or contrast of the product.
Phew! My first tutorial with screen shots. Let me know if it's useful, and if I've made any mistakes.