There is usually an example circuit in the datasheet. I start there. Many ics now also sell that example circuit on a pcb you can buy from the same supplier y

There is usually an example circuit in the datasheet. I start there. Many ics now also sell that example circuit on a pcb you can buy from the same supplier you buy your ics from. Then to make your own custom thing you just start with that example circuit, change it or add to it as needed for your specific application, and then you can physically make those same modifications or additions to the example circuit board you bought and test your design before ordering custom boards. It's basically like tracing an outline of a drawing with tracing paper and then filling it in with color. You trace the example design, add your own color.