Tainan is manageable on foot for the historic core, but the city is spread out enough that you will want some transport for covering the distance between the old centre and the Anping district, about four kilometres to the west. Cycling is excellent: the city has a YouBike bike-share network with docking stations throughout the centre, and the flat terrain and relatively gentle traffic make it the most pleasant way to explore.
Taxis are plentiful and not expensive. Ride-hailing apps (Uber and local equivalents) work here. City buses exist but the network is confusing and coverage of tourist areas is uneven — if you're staying more than two days, a day rental of a scooter or bicycle makes considerably more sense for anything beyond the immediate centre.
The Tainan TRA station is the arrival and departure point for trains. The BRT and light rail system is being expanded, but as of the mid-2020s most visitors rely on cycling and taxis for practical transport. The National Cheng Kung University campus in the east of the city is a 15-20 minute walk from the historic core and often passed through on foot.