How can I set a product as "New" or "Sale" in Magento 2

1. How to mark a product as "New" in Magento 2

Step 1. Go to Catalog > Products and select product to edit.

Step 2. In General tab you will find two fields: 'Set Product as New from' Date and 'Set Product as New to' Date. Fill them and press save.

Step 3. Go to System > Index management and if necessary reindex your catalog. More details on how to reindex your store here: How to reindex your Magento 2 store from admin or SSH / CLI

Step 4.  If the product is not showing up as New at this point, try clearing Magento cache from System > Cache management > Flush Magento Cache or other 3rd party caches that you are using. 

2. How to mark a product as "Sale" in Magento 2

Step 1. Go to Catalog > Products and select product to edit.

Step 2. In General tab go to Price > Advanced Pricing and set a sale price and the sale interval.

Step 3. Go to System > Index management and if necessary reindex your catalog. More details on how to reindex your store here: How to reindex your Magento 2 store from admin or SSH / CLI

Step 4.  If the product is not showing up as New at this point, try clearing Magento cache from System > Cache management > Flush Magento Cache or other 3rd party caches that you are using.