关于MDN上local library的route问题

Question

// Display Author create form on GET.
exports.author_create_get = function(req, res) {
    res.send('NOT IMPLEMENTED: Author create GET');
};

// Handle Author create on POST.
exports.author_create_post = function(req, res) {
    res.send('NOT IMPLEMENTED: Author create POST');
};

为什么create会有post和get? create不就是一个post方法吗？
能否解释以下注释。。

// Display Author delete form on GET.
exports.author_delete_get = function(req, res) {
    res.send('NOT IMPLEMENTED: Author delete GET');
};

// Handle Author delete on POST.
exports.author_delete_post = function(req, res) {
    res.send('NOT IMPLEMENTED: Author delete POST');
};

为什么delete会有post和get??

// 此处为什么需要一个get？
router.get('/book/create', book_controller.book_create_get);

// 我能过够理解这个
router.post('/book/create', book_controller.book_create_post);

谢谢！