A via ferrata is a fixed steel cable bolted to a rock face, with iron rungs, ladders or pegs as foot- and hand-holds. You clip a Y-shaped lanyard with two carabiners to the cable and re-clip past each anchor. The kit also includes a harness, a helmet, and on harder routes a short rest sling.
On many Dolomites trails the cable is short and almost flat — what Italians call a sentiero attrezzato (equipped path) rather than a true ferrata. These you can hand-walk safely. The named ferratas with vertical exposure are a different category and demand the full kit.