Schema::create('cursos', function (Blueprint $table) {
    $table->bigIncrements('id')->unsigned();;
    $table->bigInteger('categoria_id')->unsigned();
    $table->bigInteger('dono_id')->unsigned();
    $table->string('nome');
    $table->string('descricao');
    $table->float('valor');
    $table->string('imagem');
    $table->timestamps();
});

Schema::create('aulas', function (Blueprint $table) {
   $table->bigIncrements('id');
   $table->bigInteger('curso_id')->unsigned();
   $table->string('nome');
   $table->text('descricao');
   $table->time('duracao');
   $table->string('link');
   $table->timestamps();
});

Schema::table('aulas', function (Blueprint $table) {
    $table->foreign('curso_id')->references('id')->on('cursos');
});

[...]
    public function aulas()
    {
        return $this->hasMany('appAula', 'curso_id', 'id');
    }

[...]
public function curso()
{
    return $this->belongsTo('appCurso', 'curso_id', 'id');
}

Route::prefix('usuario')->namespace('Usuario')->group(function () {
        [...]
        Route::prefix('curso')->group(function(){
            Route::get('/{cursoid}/aula/{aulaid}', 'CursosController@aulas')->name('curso.aula');
        });
    });

public function aulas($cursoid,$aulaid)
    {
        $curso = Curso::findOrFail($cursoid);
        $aula = Aula::findOrFail($aulaid);
        $aulas = $curso->aulas;
        return view('usuario.aula',compact('curso','aulas','aula'));
    }