and also their specifications. These specifications will dictate design.
Right now you are at PCB design. Work on that right from schematic trough netlist, component layout, manual and auto, routing etc till the final artwork, its printing, etching, masking, drilling etc.
PCB deisgn have following steps broadly -
1) Analyze the functionality that you want to implement in the baord and select appropriate Chips and components
2) Development of schematic diagram ( Circuit that you want)
3) Then generate the netlist and import that netlist in to PCB routing editior
4) Route the complete circuit on the PC using PCB routing editor
5) then generate garber file and send that files to PCB manufactors
Work on the sample PCB projects that come along with PCB design software package. For a PCB designer value of components does not make any difference. Only the footprint does...