Tether (USDT) is a stablecoin, i.e. a crypto currency which is pegged (tethered) 1 to 1 with the US Dollar. The Digital Financial Ecosystem discussed above can only be via entered by an exchanging Tether. To buy Tether you need to open an account with a crypto currency exchange. Some crypto currency exchanges allow you to exchange fiat money for crypto currency as well as exchange one crypto currency for another.
There are many good exchanges to choose from and most list Tether, however for ease of use, accessibility of support, simplicity and excellent security, you might want to look at the Dacxi exchange.
Daxci does not currently support deposits in US dollars so if you need to use US dollars you may wish to consider opening a different exchange account such as Coinbase which you can join here.