It is not a problem to import a single product to Magento 2, since you have all the necessary tools under System -> Export. But if you need to move configurable products from the old site, it may take a lot of time and effort, since in this situation the import procedure is much more sophisticated. However, it is still possible to import a configurable product with its simple products to Magento 2, and below we shed light on what is necessary for a successful import. Note that the following article only briefly describes the process. For further information on how to import configurable products to Magento 2, read this guide: The Complete Guide to Magento 2 Configurable Products.