Code used in System Lifecycle tutorial video on the Turbo Makes Games YouTube Channel - https://youtu.be/pViD_h8NXf0

CapsuleTag.cs

using Unity.Entities;

namespace TMG.SystemLifecycle
{
    [GenerateAuthoringComponent]
    public struct CapsuleTag : IComponentData {}
}

IntroSystem.cs

using Unity.Entities;
using UnityEngine;

namespace TMG.SystemLifecycle
{
    [DisableAutoCreation]
    public class IntroSystem : SystemBase
    {
        protected override void OnCreate()
        {
            Debug.Log("OnCreate()");
        }

        protected override void OnStartRunning()
        {
            Debug.Log("OnStartRunning()");
        }

        protected override void OnUpdate()
        {
            Debug.Log("OnUpdate()");
            Entities.WithAll<CapsuleTag>().ForEach((Entity e) =>
            {
                
            }).Run();
        }

        protected override void OnStopRunning()
        {
            Debug.Log("OnStopRunning()");
        }

        protected override void OnDestroy()
        {
            Debug.Log("OnDestroy()");
        }
    }
}

SpawnCapsuleData.cs

using Unity.Entities;

namespace TMG.SystemLifecycle
{
    [GenerateAuthoringComponent]
    public struct SpawnCapsuleData : IComponentData
    {
        public Entity CapsulePrefab;
    }
}

SpawnCapsuleSystem.cs

using Unity.Entities;
using UnityEngine;

namespace TMG.SystemLifecycle
{
    public class SpawnCapsuleSystem : SystemBase
    {
        private SpawnCapsuleData _spawnCapsuleData;
        private Entity _spawnedCapsule;
        
        protected override void OnStartRunning()
        {
            _spawnCapsuleData = GetSingleton<SpawnCapsuleData>();
        }

        protected override void OnUpdate()
        {
            if (Input.GetKeyDown(KeyCode.Alpha1))
            {
                _spawnedCapsule = EntityManager.Instantiate(_spawnCapsuleData.CapsulePrefab);
            }

            if(Input.GetKeyDown(KeyCode.Alpha2))
            {
                EntityManager.DestroyEntity(_spawnedCapsule);
            }
        }
    }
}