Carlos: a feature wall is when you colour one wall differently to the rest of the walls in the room. It's a nice way to create contrast.
Seabody: Complimentary colours are a good start, but there are lots of other combinations which work too. Speaking of which, there's a great guide to working with colours on the official site
here. You might need to try a few different colour schemes before you find one you like, but there's no reason you should just stick to complementary colours
. Here's some examples:
I don't think any of these look bad, and only the last picture used complimentary colours (pink and green). Don't forget to match the skirting boards!