Convert multiple Shapefiles in Raster in R(and then plot it)

I'm trying to convert several shapefiles in rasters at the same time. I already was able to read the shapefiles by doing this:

library(maptools)

shps <- dir(getwd(), "*.shp")
for (shp in shps) assign(shp, readShapePoly(shp))
for(j in 1:245)
{
New<-readShapePoly(shps[j])     
}

But now, I don't know how to convert these to raster and then plotting it. I tried the commands on this page, but I only obtain errors