If you’re getting started in street photography, you will want to use a zoom lens, rather than a prime. An 18-55mm kit lens (or similar) will be fine to start. I recommend planning to move to a prime lens once you have more experience.
The reason for this is that they are (usually) sharper than zoom lenses and shooting consistently at one focal length will help you to develop your own style. When you’re ready to invest in a prime lens, you can look back at the metadata of all the street photos taken with your zoom lens and observe what focal length you used most often. This will help inform your decision making for which focal length to choose when buying a prime lens.