The A1 is the center cross. A2 is the left and right crosses, A3 is the top and bottom crosses.
B1 is the triangular corner coming from the center cross. C1 and C2 are the triangular fillers that look like shafts of light meant to radiate from the crosses. You will ultimately need 4 sets of C1 and C2 per panel. D1 is the small corner square.
The Large Connector (Lconnector file) is used to lock almost every piece together.
The Small Connector is used for the D1 corner squares.
Glue is suggested to connect the pieces as well as putty or sticky gelatin for mounting on the wall.

I would print with whatever your preferred settings are. The panels can be shrunk or expanded according to your tastes but the connectors will need some alterations. It can also be put together with glue and no alterations. If you are having trouble with the fit then I suggest lightly sanding the sides or tightening your print settings. They were made with a slight gap to facilitate fits better but ultimately (as with any puzzle of a print) it falls to the machine to accurately form the panel pieces.

On pretty much every main form of social media my profile is @ printingwithyou

Hope you have a great rest of your day and you enjoy the wall panels. If you do print them, I'd love to see what color combination you went with.