Just read the part # off the parts in the circuit and Goo search a datasheet.
Things like the "Capacitor Polarized", you would get the value and voltage, and look for a non-polarised version so you don't have to worry about which way you put it on the PCB.
EEVblog has heaps of vids on how to design stuff, like picking parts, finding parts in Digikey, PCB design for manufacturing, etc. Most are at the start.
Selecting parts
Designing - part selection.
