Tony R. Kuphalt's "Combinational Logic Functions"
Read this chapter, which describes the design of several components using logic gates, including adders, encoders and decoders, multiplexers, and demultiplexers. This chapter also mentions ladder logic. If you are not familiar with ladder logic, you may also optionally read Chapter 6 as a reference.
Click http://www.ibiblio.org/kuphaldt/electricCircuits/Digital/DIGI_9.html link to open resource.