the stereo speakers dont have rca plug but just the wire ....

you don't want to resolve it because you are attemtping to hook up home stereo speakers for referencing. At least buy some cheap reference monitors with RCA inputs and some good headphones. If you're dead set on your present course though you'll have to cut one end of the RCA cable and wire it to your speakers. 
 
Edit: Mokko, I in no way intened to come across as being rude or belittling to you in anyway, so accept my apologies if that's how it came out. I only meant to get across that if you were indeed trying to hook up a regular pair of home stereo speakers to your interface for the purpose of monitoring, it's not an ideal solution. On the other hand, if that's all you've got then that's all you've got. There are cheap desktop monitors though that have RCA inputs or you can splice the wires together to hook up the ones you already have. A better solution though would be to use a decent set of headphones. Shure, Sony, etc, all make good cans for $99 that will give you a much better shot at a good mix. Good luck and again I apologize if you thought I was being rude.