Most stations have easily deciphered signage - you shouldn't have any problem finding your track, and there usually are numbers on the ground indicating the car numbers. I don't recall seeing porters but there are railroad employees who can point you in the right direction....

You can just show your ticket to anyone in a uniform, and 99% of them will point you in the right direction.

If you are on a shinkansen it's even easier, as they usually have an icon with the profile of the shinkansen (it looks more like an airplane profile) vs the flat front view of a regular train on the overhead directional signs in the station.

Shinkansen also have different tracks, so the platforms are normally grouped separate from the other platforms.