In order to get a reasonable interesting operating potential, you should have at least four tracks, or "destinations". (More is better, but don't crowd it!) I recommend that three of them should
be general-purpose tracks, so any type of car can use them, for example:
Passenger Track. Just off the mainline where you place a station for a weekly passenger train, possible a combine passenger and freight office.
Team track. The freight office is another name for this. If the customers come to the railway with their goods, it can be anything.
Interchange. This is where cars go "off and on" the layout. Can be either a fiddle yard where you do it by hand, a set of hidden tracks where you drop off and pick up cars or a full blown staging
yard.
The fourth should be connected to an industry of some kind, so there's an obvious, visible purpose to the cars there. Some examples are:
A industrial group of sidings where you have more than one customer with trains delivering and shipping goods. A warehouse for furniture, a limber yard, a cement plant are just some of the possible
industries sharing a siding.
A mine. Empty hoppers in, loaded hoppers out. Sometimes a boxcar with supplies arrives.
A sawmill. Flatcars with logs in, boxcars with finished products out.
Petroleum terminal or chemical industry. Tank cars out and in.
Quay. Anything can come and go on ships.