"selling price 1.3633" means that the selling price of 1 euro in this transaction is 1.3633 USD, while "buying price 1.3635" means that the buying price of 1 euro is1. The difference between the buying price and the selling price here is called the spread. From here, we know that the spread between the euro and the dollar is 2 points.

When trading at "selling price 1.3633", it is believed that the value of the euro will fall relative to the US dollar. When trading at this price, the exchange rate of the euro against the US dollar will fall and make money;

When trading at "buying price 1.3635", it is believed that the euro will appreciate against the US dollar. When the transaction is made at this price, the exchange rate of the euro against the US dollar will rise to make money.