Filament refers to the roll of plastic used in FDM printing. There are thousands of choices out there for filament. It can be hard to choose one when you are getting started. Material type, Diameter, color, and finish are all factors in your decision. There are tons of articles out there on filament choice and we won’t rehash all of it here, but we will give you the highlights.
Diameter is easy. You can check to see what type your printer uses and just go with that. 1.75mm is most common for smaller/hobby printers.
Material type is a little more subjective, but we can tell you that PLA is what we use as it is inexpensive, widely available, easy to work with, and doesn’t off-gas toxic fumes like some other types.
Color is totally up to you, but we like grey and black as they are more forgiving to paint over.
Finish, like glossy, translucent, glow in the dark, or silky is also totally your choice too, but if you plant to paint over it, these may not be worth much thought.
To that end, we use Hatchbox Black and Grey PLA as well as Matter Hackers MH Build Grey PLA in our studio.