The Inspector lets you configure components and scripts without editing code.

[SerializeField]
private float speed = 5f;

Useful attributes:

[Header("Movement")]
[Tooltip("Player movement speed")]
[Range(0f, 20f)]
[Space(10)]
[ContextMenu("Full Heal")]

Prefer [SerializeField] private when a field should be editable in the Inspector but should not be public API.