We don’t rent a car in the UK, but instead rely on mass transportation. Figuring out the buses took me some time and even after many years, I still find myself double and triple checking the schedules. In addition, although all the schedules are online, along with every other piece of knowledge in the universe, I still take the paper booklet with me, handy for the times when there's no cell service.
The Cornwall bus booklet has a map that shows bus routes and bus numbers. You start by finding the numbers of the buses (sometimes there's only one) that go where you want to travel.
Or you can use the index. The goal is to get the bus number(s). Then you can turn to the correct page to see the actual schedules. So far, so easy.
Our bus pulls over to let a flock of sheep go by.
Always checking and double-checking.
The time schedule is the tricky part because you have to pay attention to several things at the same time. Is it a weekday or a weekend? A school day? A bank holiday? Is your schedule the most recent one because yes, they change.
If you have to connect somewhere to take a second bus (which we often do) than you have to pay attention to connection times, meaning you have to toggle back and forth between pages. Buses are almost always on schedule so it takes careful planning to make those connections. Be prepared to wait, or run for the bus, or sometimes, both.
Last resort is you just ask the driver. They're friendly.