Saving Many to Many relationship data on MVC Create view

I have some issues with a Many-to-many relationship saving the results of a create view.

I want to do a create page for a new user profile that has a checklist that lets them choose courses (many to many relationship). My view takes the records from the Courses database and shows them all with checkboxes.

Once the user posts the data, I want to update my userprofile model, and also the courses many-to-many relationship. That's the code that I have missing!

I'm new at MVC and I've been researching but I couldn't do it yet.

I am following this example: http://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/updating-related-data-with-the-entity-framework-in-an-asp-net-mvc-application

This is the model:

public class UserProfile
{
    public int Id { get; set; }
    public string Name { get; set; }
    public virtual ICollection<Courses>  usercourses { get; set; }
}

public class Courses
{
    public int CourseID { get; set; }
    public string CourseDescripcion { get; set; }
    public virtual ICollection<UserProfile> UserProfiles { get; set; }
}

public class UserProfileDBContext : DbContext
{
    public DbSet<UserProfile> UserProfiles { get; set; }
    public DbSet<Courses> usrCourses{ get; set; }
}

I also added a ViewModel:

namespace Mysolution.ViewModels
{
    public class AssignedCourseData
    {
        public int CourseID { get; set; }
        public string CourseDescription { get; set; }
        public bool Assigned { get; set; }
    }
}

This is the create Controller that populates the courses checkboxes:

public ActionResult Create()
{
    PopulateCoursesData();
    return View(