Сниппеты для работы

$file = CFile::ResizeImageGet($arSection["PICTURE"], ['width'=>150, 'height'=>150], BX_RESIZE_IMAGE_PROPORTIONAL, true);
//$arItem["PREVIEW_PICTURE"],  $arItem["DETAIL_PICTURE"]

$arFilter = [
  "IBLOCK_ID"=>$arParams["IBLOCK_ID"], 
   "ACTIVE"=>"Y"
];
$arSelect = ["ID", "NAME", "DATE_ACTIVE_FROM"];
$res = CIBlockElement::GetList(["sort"=>"asc"], $arFilter, false, ["nPageSize"=>50,"iNumPage"=>1], $arSelect);
while($arItem = $res->Fetch()){
  //самый быстрый
}
while($arItem = $res->GetNext()){
 //обрабатывает детальную страницу из шаблона пути
}
while($ob = $res->GetNextElement()){
  $arFields = $ob->GetFields();  
}

$el = new CIBlockElement;
$arProps = array();
$arProps[$propId]= $propValue;
//или
$arProps[$propCode]= $propValue;


$arItem = [ 
 "MODIFIED_BY"    => $USER->GetID(), // элемент изменен текущим пользователем
  "IBLOCK_SECTION" => false,          // элемент лежит в корне раздела
  "PROPERTY_VALUES"=> $arProps,
  "NAME"           => "Элемент",
  "ACTIVE"         => "Y",            // активен
  "PREVIEW_TEXT"   => "текст для списка элементов",
  "DETAIL_TEXT"    => "текст для детального просмотра",
  "DETAIL_PICTURE" => CFile::MakeFileArray($_SERVER["DOCUMENT_ROOT"]."/image.gif")
  ];
$res = $el->Update($id, $arItem);

global $USER;
$arParamsCode = ["replace_space" => "-", "replace_other" => "-" ];
$el = new CIBlockElement;
$arProps = array();
$arProps[$propId] = $propValue;
//или
$arProps[$propCode]= $propValue;

$arItemNew = [    
    "NAME" => $arArticle["title"],
    "DETAIL_TEXT" => $arArticle["text"],
    "DETAIL_TEXT_TYPE"=>"html", //"text"
    "IBLOCK_ID" => $iblockId,

    "PROPERTY_VALUES" => $arProps,
    "IBLOCK_SECTION_ID" => false,
    "ACTIVE" => "Y",
    "MODIFIED_BY"    => $USER->GetID(),
    "CODE" => Cutil::translit( $arArticle["title"], "en", $arParamsCode )
];
if($id = $el->Add($arItemNew)) {
    echo "New ID: ".$id;
}
else {
    echo "Error: " . $el->LAST_ERROR." ";
}

\Bitrix\Main\Loader::includeModule('iblock');

$element = \Bitrix\Iblock\Elements\ElementCatalogTable::getList([
   'select' => ['ID', 'NAME'],
   'filter' => [
      'ID' => $elementId,
   ],
   "cache" => ["ttl" => 3600], //кэширование
   "limit" => 10
])->fetchObject();
foreach ($elements as $element) {
    // ...
}
 

$element = \Bitrix\Iblock\Elements\ElementCatalogTable::getByPrimary($elementId, [
    'select' => ['ID', 'NAME', 'DETAIL_TEXT', 'DETAIL_PICTURE', 'ARTNUMBER'],
])->fetch(); 
var_dump($element); //массив

$arFilter = [
   'IBLOCK_ID' => $arParams['IBLOCK_ID'],
   '>LEFT_MARGIN' => $arParentSection['LEFT_MARGIN'],
    '<RIGHT_MARGIN' => $arParentSection['RIGHT_MARGIN'],
    '>DEPTH_LEVEL' => $arParentSection['DEPTH_LEVEL']
]; // выберет потомков без учета активности
$bShowCount = false; //количество элементов в разделе
$arSelect = ["UF_NAME_EN"]; //список полей

$rsSect = CIBlockSection::GetList(['left_margin' => 'asc'],$arFilter,$bShowCount,$arSelect);
while ($arSect = $rsSect->GetNext()){
       // 
}

$res = CIBlockElement::GetProperty($iblockId, $elemId, "sort", "asc", ["ID" => $propId]);
while ($arValue = $res->GetNext()){                            
//
 } 

$propertyEnum = CIBlockPropertyEnum::GetList(["DEF"=>"DESC", "SORT"=>"ASC"], ["IBLOCK_ID"=>369, "CODE"=>"STAGE"]);
$arStages = [];
while($arStage = $propertyEmum->GetNext()){
   $arStages[$arStage["XML_ID"]] = $arStage["ID"];         
} 

use Bitrix\Main; 
use \Bitrix\Main\Loader;
define("LOG_FILENAME", $_SERVER["DOCUMENT_ROOT"]."/bitrix/php_interface/log.txt");

AddEventHandler("iblock", "OnBeforeIBlockElementAdd", "MyOnBeforeIBlockElementAdd");
AddEventHandler("iblock", "OnBeforeIBlockElementUpdate", "MyOnBeforeIBlockElementUpdate");

AddEventHandler("catalog", "OnBeforeProductAdd", "MyOnBeforeProductAdd");
AddEventHandler("catalog", "OnBeforeProductUpdate", "MyOnBeforeProductUpdate");


function MyOnBeforeIBlockElementAdd(&$arFields){      
}

function MyOnBeforeIBlockElementUpdate(&$arFields){    
}

function MyOnBeforeProductAdd(&$arFields){
    if (@$_REQUEST['mode']=='import'){//импорт из 1с          
    }
    return true;
}
function MyOnBeforeProductUpdate($id,&$arFields){
    if (@$_REQUEST['mode']=='import'){//импорт из 1с          
    }
    return true;
}

require_once($_SERVER['DOCUMENT_ROOT'] . "/bitrix/modules/main/include/prolog_before.php");

if(!defined("B_PROLOG_INCLUDED") || B_PROLOG_INCLUDED!==true)die();

$APPLICATION->AddHeadScript('/bitrix/templates/.default/js/jquery.min.js');
$APPLICATION->AddHeadScript($this->GetFolder() . '/script.js');
$APPLICATION->SetAdditionalCSS('/bitrix/templates/.default/css/jquery-ui.css');

use Bitrix\Main\Page\Asset;

Asset::getInstance()->addCss($this->GetFolder() . '/dealer_client_choose.css');
Asset::getInstance()->addJs(SITE_TEMPLATE_PATH . '/assets/js/script.js', true);

<?=$component->GetPath()?>/component.php
<?=$this->GetFolder()?>/ajax.php //обращение из template.php к файлу ajax.php в папке шаблона

<?ob_start();?>
Hello Nika
<?
$hello = ob_get_contents();
ob_end_clean();
?>
Before hello text
<?=$hello?>

echo LOG_FILENAME;

//получить содержимое
$data = file_get_contents(LOG_FILENAME); 
var_dump($data);

//очистить
file_put_contents(LOG_FILENAME,""); 

<iframe 
   style="width:100%;height:325px;" 
   frameborder="0" 
   allowfullscreen="1" 
   allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" 
   title="Video Title" 
   width="640" 
   height="365" 
   src="https://www.youtube.com/embed/MisjXqBpKdg? --тут не надо переноса
     controls=1&modestbranding=1&rel=0&showinfo=0&loop=0&fs=1&hl=en&enablejsapi=1& --тут не надо переноса
     origin=https%3A%2F%2Fmysite.ru&widgetid=1">
</iframe>