How do I buy tickets for “smaller” trains, not shinkansen?

I got the JR pass, so my understanding is that shinkansen is included in the pass, but how do i pay for trains and busses that are not included? where can i buy tickets in advance?

asking because i’m wondering if i should cancel my JR pass

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For example, at some point I’ll do Himeji > Uno.

I think Himeji > Okayama is a train that is included in the JR pass, right?
And Okayama > Uno is a bus, right? how do i buy this bus ticket in advance?

Another example is Kyoto > Nara (if i dont get the JR pass), I see it’s on the “Kintetsu Limited Express”, how do i buy that ticket?

Thanks

by idontloveanyone