When you create a new tax rate, it is NOT automatically applied to any existing Products. If you'd like to tax all your Products at a location, or just some of your products it's easy to do!
Just click "Apply Tax to Products" at the right of the Tax Rates page:
You can use filters and searches to add the products you would like to assign that tax to or you can choose to add all products.
Remember - first you will want to 'Load All' products
Once all products that you want to be assigned to that tax rate are on the right-hand side click Save.