2.what is the exact differnce between solid and surface modelling
Pull direction refers to the draft angle on a tapered part. What direction will you pull the tool to release the part? What direction would the ejectors strike the part to remove it from the tool? Think of an ice cube tray. Ice cubes only leave the tray in one direction due to draft angle.
Solid models have properties such as mass and density. Surface bodies may surround a given volume, or have a surface area, but the surfaces have no thickness and therefore no mass or density.