A Gerber file for each layer (copper layers, solder mask, legend, etc).

All Gerber files must have the same origin, orientation, etc.
Images shall not be mirrored, scaled, or rotated.

Gerber files must be in “Extended Gerber” format, preferably in 6.6 MM format, with leading zero suppression and absolute coordinates.

We also recommend using Gerber X2 extensions. Drill (template) drawings are not needed.