Kigali is a hilly city and walking between neighbourhoods can involve more climbing than you expect, but within any given area walking is perfectly safe and pleasant. The central areas — Kiyovu, downtown, the areas near the genocide memorial — are walkable once you have your bearings.
For longer distances, moto-taxis (motorcycle taxis) are the fastest and cheapest option. All moto drivers are required by law to carry a spare helmet for the passenger, and helmets are mandatory — do not get on a moto without one. Agree on the price before you get on; a trip across the city should cost 500-1500 Rwandan francs (roughly 0.50-1.50 USD). Motos are banned in the city centre during peak hours on weekday mornings and evenings.
Regular taxis are plentiful and easier than motos for luggage or longer trips. Established apps like SafeMotos and Yego Cab operate in Kigali. The Rwandan bus system (Twegerane) connects the main thoroughfares but is slow and confusing for first-time visitors. Car rental is available at the airport for those planning to drive to the national parks.