Your wallet works before it exists
You get an address straight away and people can send money to it right now. The wallet itself gets built automatically the first time you use it, as part of the same transaction. Nothing extra to do, nothing extra to pay.
The fee is based on a 15 minute average
Float works out what the fee is worth in your token using the average price over the last 15 minutes, then adds 15%. Using an average means nobody can move the price for a second to overcharge you. The current reading is at the top of this page.
You get change back
Nobody knows the exact fee until the transaction is done, so float holds a bit extra up front, then charges what it actually cost and sends the difference straight back to you in the same token. The change you see on this page is read from the transaction itself, not estimated.
If you are short, nothing happens
If your balance will not cover the fee, the transaction is refused before it starts. Nothing is sent, nothing is charged, and this page tells you exactly how much you need to add first.
Float pays the chain for you
Float keeps a pot of ETH and pays the chain out of it on your behalf, then takes the equivalent from you in your token. That is the whole trick, and it is where the name comes from.