The word guarantee just refers to a promise that certain conditions will be fulfilled. We can use it with products, or with things that are not products:
All our products come with a 30-day money-back guarantee.
I guarantee you will enjoy the experience.
We guarantee the accuracy of the information in our reports.
A warranty is a specific type of guarantee - it is ONLY used for products, and it is a promise that if the product breaks, the seller or manufacturer will fix it or replace the product.