Once on the quote module click on “Product” button on the top menu or go directly to “Product / Service Information”.
To add a product or service to your quote: You can do a search directly from the product/services combo box by entering the name of the product or you can browse the product category and then the product combo box. Then add a quantity and click the "Add" button. The units, price, and total are taken from your product catalog. You can add a discount, promotion and product comment. You can as well mark the product or service as tax exempted.
To add a new product to your catalog and te to your quote click on "+" t. A new screen will open so you can enter the product or service information.
For more information on how to create and add product catalog to your catalog visit this link How to add a product or service? (3 methods)
If you want to create promotions check this link How to add promotions?