'train services in general' being inner city ones or going from city to city? Anyway shinkasen has reserved cars for tickets bought in advance but you can buy them at a station and wait there IIRC.
Yeah, Shinkansen is reserved seat only, but you can get a ticket and usually take the next train - except for really busy connections, e.g. Friday evening or Golden Week.
I always walked into the JR booth flashed my Green pass told them where I was going and got on the next train.
Thanks guys. Yeah I was talking about inter city connections. I will have to go from Tokyo to Takayama, from Takayama to Kyoto and from Kyoto back to Tokyo. Might just stop by Tokyo Main Station on my first day and try to sort transportation out.