question on allegro?
1. A negative plane is a plane that has uses "positive" data to represent non-copper. The gerber file is then inverted by the service buro that prepares the photo plots. Thus, such a plane data will be less bytes that a positive one.
2. A plated through hole has copper in it. This enables a copper connection from the top to the bottom side. You can not make multi layer PCB's without plated holes. A via hole is always plated. If your design is very simple it may not need double sided boards and thus no through hole plating.
3. The service buro sometimes needs this. At least where I live in scandinavia this is no longer rerquired. The drill files and their descriptions is normally good enough.
4. Solder mask = green lacquer on the PCB that should prevent solder from escaping from the solder pads in the soldering process. The mask also acts as insulator.
5. The paste mask is a separate layer not used in the PCB. Instead, this layer goes to the assembly plant that produces a metal stencil placed upon the pcb and then used for smearing solder paste onto the naked board.
6. The Assembly outline is used in (paper) drawings to show detailed information about pinning, orientation, dimensions and such. This layer is never printed on the board. The silk screen layer is the (text) layer that normally gets printed on the board. It contains reference designators, pin numbers, warning texts such as "High Voltage" and board part number.