The train takes you through stunning land scape and local neighbourhoods. You can buy an MTS Compass (Tap and Ride) Card from ticket machines at stations. Routes are marked quite clearly. Check out more information and the map at this site to plan your trip https://sdmts.com/schedules-real-time-maps-and-routes/trolley.
It is quite easy to navigate and use the public transport in this city, and if you are lost do ask around. The people in San Diego are generally helpful and friendly.