AM are sockets for AMD's CPU product. Basically every AM2 and AM3 CPUs are compatible to one big socket platform. The only segregation came as features that gets enabled or disabled.
The FM1/FM2 sockets are for APUs only. The FM1 for every APU prior to Richland architecture. FM2 is for the latest gen APU. Price segmentation basically about the same as AM sockets.
Every AM board carries 3 digit numbers. Number 9 on 1st digit signifies higher feature and 7 will be the lowest and bare necessities. For FM boards, also about the same story.
Every FM board are mandated to include some video output, meaning it must have dGPU enabled.
FX series is the latest CPU series for AM boards.
APU price segmentation dictated by its numerator. Started with an 'A'. The higher the number, the more powerful the GPU/CPU included will gets.