What's a spoon, really? A tiny bowl with a long handle so that we don't have to drink clumsily from a larger bowl.
We use it for soup, but that's just the elegant modern way to do it. The original way (which survived in rural areas well into the 19th century) was to pick up the whole bowl and chug it down. Sticklers for good usage insist that we should say we "drink" soup, rather than "eat" it, but in the old days that went without saying.
Spoons are officially intended for liquid or semiliquid food, so we use a spoon for pudding or ice cream (hence the expression "X could eat Y with a spoon," meaning X considers Y a luscious treat). But we use a fork for pie, because it's a pastry, a distinction that has infuriated many a small child who wanted to get all of a pie's drippy fruit filling.
Spoons are older than forks, because nature provides them. Where people live near the sea, sea shells are often used as spoons. Gourds and sections of bamboo have been used too, and spoons are easy to carve out of wood. In a few places, as among the Native Americans of the Pacific Northwest, the "spoon" might actually be almost flat, like a paddle, because its real use was to fish out solid bits of food for the honored guest.
In many parts of the world, people eat out of a communal plate and even take soup from a common bowl. Obviously, this poses a risk of spreading disease.
But people have ways of getting around that. In Central Asia, for instance, the soup spoon has a remarkably wide bowl--sometimes it looks like two bowls side by side--and etiquette requires that you scoop away from you into the common bowl of soup or yogurt. So the part of the spoon that goes into the soup is not the part that goes into your mouth. Clever.