If you open online banking, you can purchase foreign exchange from online banking.
You need to open a foreign exchange account at the counter.
LZ, if you ask a supplementary question, can you ask it under our answer? As soon as you add one, we will revise the original answer. There will be a problem with the time, so it is not convenient for you to understand the answer.
Buying and selling are not simultaneous, but can be traded in both directions, not for you to buy and sell at the same time.
Of course, it is also allowed to buy first and then sell, or sell first and then buy.