Join two tables if many to many relationship

Hi developer,

I am new Asp.net 5 with latest version.

I am following the instruction as below:

http://docs.efproject.net/en/latest/modeling/relationships.html#many-to-many

In PostController.cs:

[HttpGet]
public IEnumerable<Post> GetPosts()
{
   return _context.Posts;
 }

How to join two tables (From Post to Tag) if many to many relationship?

I am waiting for your response.
Thanks