KiCAD - Free electronic design automation (EDA) program. Open source and sponsored by CERN. Excellent entry point for circuit board design for prototyping and production.
Bare circuits are fragile, so they must be strengthened and protected at many levels.
Consider the circuit board, solder mask, conformal coating, assembly potting, and structural enclosure.
Consider the air gaps in the circuit board (ex. thru-holes), vapor permeability of materials in the circuit assembly, mounting strength of the assembly within the enclosure, and the penetration of foreign particles into the enclosure.
Discrete electrical parts are single element circuits like resistors, capacitors, inductors, and transistors.