All you've got to do is construct a full adder cell, then add the partial products wich can be produced with AND gates (like you do with paper and pencil). This link might be helpful: https://en.wikipedia.org/wiki/Binary_multiplier
thank you very much.. it was very much useful actually i used two half adders but it turned out to be a 2-bit multiplier with sign bit as B2A2 thnks a lot..