To add a new product, in the main page, Go To More > Products > New

Important fields while creating product:

Product Type: For physical products, type must be 'Inventory item' and for services, type must be 'Services'.

Product Family: Its a broader category for products. For example in food trading business, you might have 'Food'  as one product family, 'Beverage' as another product family. 

To create a new product family Go To Setup >  Objects and Fields > Object Manager > Product > Fields & Relationships > Product Family > in Product Family Picklist Values click New > add the names in the box > Save

Parent Product: If you have sets of products that are related, you can create parent and child products.

Illustration: In textile industry, a cloth of same brand and design may have different sizes. Cloth of each size like Small, Medium and Large can be Child Products where as main brand and design will be parent product.

The parent product must be created before you can create child products. 

Active: Product should be active. 

Tax Family: Select Tax Family. 

To know on how to create tax families refer Setting Up Taxes.

Class: If you want to associate a class to a product, select class. When you associate a class to a product, while creating transactions like purchase order, sales order etc, once you select the productclass will be auto populated .  

To know more about class refer Class

Quantity Unit of Measure: Unit of measure of the product like KG, Litre, Gram, Quintal  etc. This will be primary unit of measure in which inventory records will be maintained for the product.  

To add a new unit of measure Go To Setup > Object & Fields > Object Manager > Product > Fields & Relationships > Quantity Unit of Measure > in Quantity Unit of Measure Picklist Values click New > add the names in the table > Save

Enable Batch Tracking: Click to enable batch tracking for the product.

General Ledger Mapping : You can leave this section blank. System will auto populate it for you.

Sync Information : You should not do any changes in this section.