What is the difference between inclusive and exclusive tax on add product page?

Inclusive tax method means that tax is already included in the price. Exclusive tax method means that tax is not included in the price and should be calculated/added separately.

For example:

Product Price 100 and Tax 10%
Inclusive tax method: Price 90.91 and Tax amount: 9.09 = 100 (total price with tax) Exclusive tax method: Price 100 and Tax amount: 10 = 110 (total price with tax)