The "amount" field determines the volume or size of the order - i.e. how much is bought or sold. Volume is measured in terms of the "amount currency," which is set to the base currency by default, but can be changed to the quote currency. It is important to remember that the "amount" field only determines how much is being bought or sold and does not determine what is being bought or sold.
Example: creating an order by inputting 1 in the amount field to buy 1 BTC at a rate of $7,624.90 per BTC.
Example: creating an order by inputting 5000 in the amount field to buy $5,000 worth of BTC at a rate of $7,624.9 per BTC.
If you open up a spot position on margin it would look the same with the only difference being the ratio of leverage being used.
Example: creating a limit order to go long BTC on $3,000 worth of BTC/USD using 3x leverage that executes once the price drops to $8,185.50.