Magento2 – Understanding Order ID and Increment ID

The syntax should be like that:

{
  'searchCriteria[filter_groups][0][filters][0][field]': 'entity_id',
  'searchCriteria[filter_groups][0][filters][0][value]': '1, 2',
  'searchCriteria[filter_groups][0][filters][0][condition_type]': 'in'
}

but seems, there are bugs.

https://github.com/magento/magento2/issues/2892

https://github.com/magento/magento2/issues/3411

and

https://github.com/magento/magento2/issues/3018

The standard collections are actually very similar. There are other similar structures, but for products you can load them in and load them just like Magento 1. Just like in Magento 1, if you are using the collection via iteration you do not have to load it as it's done implicitly.

As always in Magento 2, you should be injecting classes via dependency injection in your class constructor. Plus, if you are going to create more than one instance you can add "Factory" after any class and you'll get a wrapping class that allows you to generate as many as you want.

Here is the use of both together:

/** @var \Magento\Catalog\Model\ResourceModel\Product\CollectionFactory */
protected $collectionFactory;

public function __construct(
    \Magento\Catalog\Model\ResourceModel\Product\CollectionFactory $collectionFactory
) {
    $this->collectionFactory = $collectionFactory;
}

public function yourMethod()
{
    // Use factory to create a new product collection
    $productCollection = $this->collectionFactory->create();
    /** Apply filters here */
    $productCollection->addAttributeToSelect('*');
    // Don't have to do this
    // $productCollection->load();

    foreach ($productCollection as $product){
         echo 'Name  =  '.$product->getName().'<br>';
    }  
}

With thanks to @megi for the example usage code in their answer.