Think of a SIM card as the little chip that tells your phone which network to use and lets it get a signal. For years that chip was a small plastic card you slid into a slot. An eSIM does the same job, but it is already inside your phone. There is nothing to swap.
Instead of inserting a card, you install a profile. You scan a code or tap a button, and your phone downloads the network settings. That is the whole idea. Once it is on, your phone connects to a Bolivian network just like a local would, and you pay one fixed price up front.