Hello Patricia,
It sounds a though you need a new sponge bar. Use the handle on the latch tool to push it out and check its condition. There should be about 1/4" of foam above the metal all the way along. If the foam is not deep enough it will not press down firmly enough on the needles and they will be in the wrong position to knit properly.
Ebay is a good place to get replacements or you can refurbish the old one - look at knittsings blog. I bought some 1/2" foam on ebay and followed these instructions and am very happy with the result.
The plating yarn feeder is a device which enables you to knit two yarns together - one will show on the plain side of the knitting and the other will show on the purl side.
Sue
February 2010