Data Annotations are attributes applied to entity classes and properties to configure the model and validation rules.
Common annotations:

public class Product
{
    [Key]
    public int ProductId { get; set; }
    [Required]
    [MaxLength(100)]
    public string Name { get; set; }
    [Column(TypeName = "decimal(18,2)")]
    public decimal Price { get; set; }
    [ForeignKey("CategoryId")]
    public Category Category { get; set; }
    [NotMapped]
    public string DisplayName { get; set; }
}

Categories:

• Key attributes: [Key], [DatabaseGenerated]
• Validation: [Required], [MaxLength], [Range]
• Schema: [Table], [Column], [NotMapped]
• Relationships: [ForeignKey], [InverseProperty]