A useful exercise pace feels purposeful but controlled. You should notice deeper breathing while still being able to speak in short sentences. A fixed speed is less useful because height, fitness, terrain, heat, and incline all change the effort.
Use the talk test
At an easy pace, conversation is effortless. At a moderate pace, talking is possible but singing would be difficult. If only a few words are possible, you are working hard. Beginners can spend most walking time at easy to moderate effort.
Pace is not the only lever
Duration, hills, and frequency also determine the training effect. Someone who cannot walk faster comfortably can extend a route or add brief inclines. Progress one variable at a time so the routine remains manageable.
Build speed gradually
After warming up, alternate one minute of brisk walking with two minutes easy for six rounds. Over several weeks, lengthen the brisk portions. Stop and seek appropriate medical advice for chest pain, faintness, or unusual shortness of breath.
Estimate energy use with the Walking Calories Calculator. For progression, read the Beginner Walking Plan, Uphill vs Flat Walking, Rest Days vs Active Recovery, and Start Here.