How to Configure TAX in the project ?

I am finding setting up TAX to be confusing.

It appears to me that a Tax Class is the same as a single product category.  Tax can then be set up but only on a per Tax Class (product category) basis.  To set up the same tax on all products would require setting up that tax for each product category separately.  Is my understanding correct or is there a way to set the tax up once and apply it to all products?

i am trying to figure what's the solution for this problem, if there are 10 categories then each tax rate has to be defined 10 times ?
and in US in each state tax rate is different for each county(zip code)
so if there are 50 different zip codes in my state with each having different tax rate then i have to store tax rate
50 tax rates X 10 Times = 500Times ?
Please provide us with the solution for this problem.

Please HELP...

PLEASE HELP ME WITH THIS ISSUE....

Indeed the operation is unclear. I need to record every sale
with a VAT (IVA) = 16% How is it done?

first provide the necessary info in:
configuration-->tax-->tax settings

then go to
configuration-->tax-->tax providers

set
Fixed Rate Tax           as default  then edit    Fixed Rate Tax

set
Fixed tax rate [%]:        as your required tax rate    eg 16