How do I model stuff like this?
Is there a name for these?
Hard surface? They're just inward extrusions. Just use the knife tool to make the shape, it's easier to sculpt hard surface nowadays with the tools available.
You extrude inwards.
Triangles. Theyre called triangles.
Aren't those bad? Or is this one of those times where it's considered ok because it's for looks/structure?
Quads are fine, triangles are fine unless the interrupt needed edge low/quad loops.
quads, tris, and ngons are fine if all you're doing is rendering "concepts" where you're expected to create models and renders quickly (aka "dirty" modeling, see Vitaly Bulgarov) and will do clean up in post.
Quads and tris are ideal for game models and baking. Some engines and baking programs just won't work with ngons.
Quads are ideal for animation/deforming because they behave "expectedly".
They're integrated scaffolding in a sense. They help reduce the weight of mechanical parts while retaining a decent amount of strength. Just make sure your "beams" follow a logical mathematical shape like these do.
triangles aaren't bad at all. The only reason to avoid them is for your own convenience, i.e adding an edge loop, or if you plan to mesh smooth. Tris are standard and completely fine.
+ if you plan to do deformations on the mesh through animation, avoid them.