Walking a 5K is around 3.1 miles since there are a little over half a mile in each Kilometer so in 5 Kilometers you'd have around 3.1 miles.
The K in 5K actually stands for and simply means 5 kilometers.
If you walk at an average walking pace the 5K walk would take you around 45 minutes to 60 minutes of time but if you speed up your walk you could likely walk the 5K walk in 35 to 40 minutes.
But if you walk slower you might take 90 minutes or 1 hour and 30 minutes to complete the 5K walk.
If you can walk a 5K distance or 3.1 miles in 60 minutes you're doing good and will improve your health if you keep doing a 5K walk often enough.