How to use join in Laravel Elocuent?

I have following two tables.

users - id,name,title
posts - id,author

where post.author = user.id

My Post model as follows.

namespace App;

use IlluminateDatabaseEloquentModel;

class Post extends Model
{
    public function users()
    {
       retu $this->belongsTo('AppUser');
    }
}

I use Project::find(1)->users

But it giving following error.

SQLSTATE[42S02]: Base table or view not found.

Can anyone please help ?