I know of two ways to feed hot water to a base board: one is to connect all sections in a series fashion and the other is to use a diverter and a bypass
To send only some hot water to each section simultainsly .
What is each method called

The first is commonly called a "series loop system". The latter is most commonly called a "monoflo system", which uses monoflo tees to divert water to the baseboard, also sometimes called a diverter system.