The centre of Skopje — from the Old Bazaar through Macedonia Square to the main pedestrian zone — is compact enough to walk. Taxis are cheap by Western European standards and widely available; use licensed taxis from official ranks or phone for one rather than taking cars that tout at the main sights. The fare across the city should be modest.
Buses serve the wider city including the suburbs, but routes can be confusing without local help. For day trips to sites outside the city — Matka Canyon, the Millennium Cross on Vodno Hill — taxis are the most practical option.