For a first time traveler at Penn Station, the best course of action is to go to the Amtrak main concourse, which is on the upper level at the 8th avenue end and has a huge Solari Board hanging from the ceiling in the middle of the hall displaying only Amtrak and NJTransit trains (no LIRR trains), as shown in the photo above.
There are all sorts of other train display boards in other parts of the station ranging from TV monitors to other Solari Boards, but avoid all those. Go to the main Amtrak concourse.
Also note that the "upper level" is one level below street level. There is very little other than entrance gates for Penn Station at the street level. The rest of the structure at that level is Madison Square Garden and Office Building (the Penn Plaza Buildings).
The upper level has the Amtrak concourse at the 8th avenue (west) end and at the 7th avenue (east) end there is the NJT concourse south of the main corridor, and stairs leading down to the LIRR concourse, which is on the lower level, north of the main corridor.
All subway entry directly into the station is into the lower level. If you walk into the station directly from a subway station without coming to the surface, you will need to go one level up to find the Amtrak concourse.
The track level is one level below the lower level and many tracks can be reached both directly from the upper level and from the lower level. There are a few tracks that can be reached only from the lower level but typically Amtrak trains do not use those tracks.
One more important thing is that there is a very useful Amtrak Information Booth right in the middle of the station at the upper level in the so called Rotunda, which can be easily identified as the area with the highest ceiling in the station structure. It is halfway between the Amtrak and the NJT Concourse on the upper level.
Hope this summary helps you find your way to the Amtrak concourse that has been mentioned several times in other posts on this thread.