We have two types of orders: limit and market.
The form to create a limit type order has 3 fields to complete: Price, Amount and Total. The Price is the value in quotation currency of one (1) unit of the base currency. Amount is the amount of the base currency we want to buy/sell. The Total is the amount in quotation currency that we are going to exchange for Amount.
The form to create a market type order has only 1 field: Amount which is the amount of the base currency that we want to buy/sell. These types of orders will take orders from the order regardless of the price until the amount of base currency entered in the Amount field is completed.