PCB Design is an exercise that may take a long time to master.
The first step to PCBs Design to choose PCB Design software.
There are many PCBs Design programs today, but you should choose what most PCBs Designers use. This includes such free and professional software as Eagle CAD and EasyEDA.
You can also go for paid versions such as Altium. Whichever you choose to use, you should start by putting together the circuit schematic. From the circuit schematic, you can then make your PCBs Design.
As you make your PCBs Design, it is important to keep in mind the capacity and the capabilities of your target PCBs Manufacturer.
They can produce 2 to 32 layer PCBs. This means that if you plan to use wellpcb.com, you are free to make your PCBs Design have as many layers as you want.