So a protein is a very big molecule. It’s so big that parts of it are attracted to other parts and cling together, think of a balloon you’ve rubbed on your hair and stuck to a wall.

These self-stickiness gives proteins a folded shape. There’s still some charge, but since the protein is folded a specific way, most other molecules don’t fit to bind to those charged areas.

However, most proteins have at least one other protein that does fit. So when a protein “meets its match” the two can bind together. When they do that, their charges mingle and change and the proteins change shape.

This act, proteins changing shape as a result of things binding to them, is how your cell “does” stuff.

So in your Golgi apparatus example, the proteins don’t know what they’re doing at all. But they have a specific shape and charge and so attract and bind specific other proteins. When they do so, they change shape and that results in the golgi doing something.