CRUD For Many-To-Many Relationship in EF Core

Hello again.

I had a problem with configuring many-to-many that it solved, thanks to @Edward Z.

Now i want to use it for CRUD operations.

How can i add related data, How can i get related data, how can i update and delete related data?

Again my models and configurations :

public class MyPost
    {
        [Key]
        public int Id { get; set; }
        public string Title { get; set; }
        public string Content { get; set; }

        public List<PostTag> PostTags { get; set; }
    }

public class Tag
    {
        [Key]
        public int Id { get; set; }
        public string Title { get; set; }

        public List<PostTag> PostTags { get; set; }
    }

public class PostTag
    {
        public int PostId { get; set; }
        public MyPost MyPost { get; set; }

        public int TagId { get; set; }
        public Tag Tag { get; set; }
    }

public class BlogDbContext : IdentityDbContext<User>
    {
        public BlogDbContext(DbContextOptions<BlogDbContext> options)
        : base(options){}
        public DbSet<MyPost> MyPosts { get; set; }
        public DbSet<Tag> Tags { get; set; }
        public DbSet<PostTag> PostTags { get; set; }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.Entity<PostTag>()
                .HasKey(t => new { t.PostId, t.TagId });

            modelBuilder.Entity<PostTag>()
                .HasOne(pt => pt.MyPost)
                .WithMany(p => p.PostTags)
                .HasForeignKey(pt => pt.PostId);

            modelBuilder.Entity<PostTag>()
                .HasOne(pt => pt.Tag)
                .WithMany(t => t.PostTags)
                .HasForeignKey(pt => pt.TagId);

            base.OnModelCreating(modelBuilder);
        }
    }

Think i want to show all posts and tags in index page, Add a post and in add form i want to add some tags to post, in list of posts when i delete a post it should delete all tags related to this post, and update post and tags.

And another question, is it fine to delete posts whene i delete a tag?