I assume many tourists want to buy something in Japan. Most of the people want to buy traditional Japanese products or souvenirs like T-shirts.
The consumption tax, similar to VAT in Europe was 8% till 30 September 2019, but went up to 10% on 01 October. However, it is still lower than EU standard which is around 20%. Then, not like in EU, the prices on the price tags are not including the tax. Therefore please keep in mind that you will be charged 10% more at the cashier.
Tax free shopping is now becoming more popular in Japan. Some stores even have bilingual staffs helping the foreign shoppers. Usually these staffs have special badge on their clothes mentioning which languages they speak.
May be the most difficult thing is the size of the clothes or shoes. Japanese sizes do not reflect the US or European sizes. Although the sizes of the clothes are mentioned as S,M, L but the bigger than L is LL, not XL. Then, LL is not similar to XL in Europe. It is rather European L, or may be US's M. Before bringing the clothes to the cashier, try them at the fitting rooms.