In a hub, all the ports are electrically connected, and only one device at a time can talk on the wire. If more then one talk, it creates a collision. That's why hub connections must be half-duplex.

In a switch, each port is isolated, and traffic from one port is selectively sent to other ports; there are no collisions. Unlike a hub, where all the ports together are in one collision domain, on a switch, each port is a separate collision domain.

In a hub, all the ports are electrically connected, and only one device at a time can talk on the wire. If more then one device talks at the same time, it creates a collision, so hub ports are all half-duplex.

In a switch, each port is isolated, and traffic from one port is selectively sent to other ports, so there are no collisions in the switch. Unlike a hub, where all the ports together are in one collision domain, each switch port is a separate collision domain. That means that each switch port can be set to full-duplex (when connected to a single device supporting full-duplex) or half-duplex (when connected to a hub or other device requiring half-duplex).