Within the quotation or the invoice you can either search on name or ID to add products. Read this article in case you want to hide the ID on your documents.
If you want to calculate different prices for different customers, Teamleader Focus offers the option of price lists. And if you want to offer different prices based on the amount your customers buy, then the option of graduated prices could be something worth discussing.
You are now all set for products. Check here for an overview of all articles on how to get started with Teamleader Focus.