And how do I surf them?

heat veins are a set of directions that point out of a scene in a specific direction, they require an  item called a toy skateboard to move around on. they can be quite difficult to get as the item requires a lot of different items to make. there might be some fun surprises if you can somehow get your hands on one ,but they are not required to play the game and access most of the normal areas.

Spoiler

heat veins are the invisible map that shows the flow of heat from one location to an other, Capitols being a spring of such veins, with heat slowly turning into liquid dust towards Death Marrow in necrovion, where its drained outside the realm.

There are locations that are only accessible via heat veins.

Darvin the lonely bot, can travel heat veins on its own.