There are three way's to add an product to an order:

1. With a barcode scanner
If you have a barcode scanner and the barcode is assigned to a product in the webshop (or in the POS) you can simply scan the barcode to add a product. 
When you want to add 2 of the same products you can eather scan the product twice or press 2 on the numpad and scan the product.

2. Search for the product in the search field. You can type the product SKU or the product name in the searchbar under the numpad and click on the "+1" Button of the product you would like to add to the order.

3. Go to Menu - Products and look for the product you would like to add to the order. Press the "+1" button of the product you would like to add.