The service is free for up to 10 calls per minute and 150 calls per day. If you need more calls please look at our licenses. Any attempts to automatically download conversion values in order to store them in your own database will get you banned.
Go to converter and fill in your email and web-address to get the code for your api. There is no need to design your widget, since you will use your own css. Copy and paste the code into your webpage and design the form with your css rules.