relationship 3 table in laravel

i have 3 table

Table Post

$table->increments('id');
$table->text('title');
$table->longText('description');

Table User

 $table->increments('id');
 $table->string('username',30)->unique();
 $table->string('email')->unique();

Table Comment

$table->increments('id');
$table->longText('comment');
$table->integer('user_id');
$table->integer('post_id');

I want to Show Post Page in footer, I want show comment by username

What can i do to relation it in laravel 5.4. Please Help explain with code.

thank for you answer.

via Chando