ConfigureServices is where you register application services with the dependency injection container. This can include framework services (MVC, Razor Pages, Entity Framework) and custom application services.

Example:

public void ConfigureServices(IServiceCollection services)
{
    services.AddControllersWithViews();
    services.AddDbContext<ApplicationDbContext>(options =>
        options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));
}