An exchange wallet is basically a website where you can buy, sell, send and receive Bitcoin or other cryptocurrencies.
A few examples are Coinbase, Coinmama and CEX.
To use cryptocurrency to fund your Galaxy account, the first step is to buy Bitcoin/cryptocurrency through one of these exchange sites.
Just set up and verify an account, use your credit card or bank transfer to buy Bitcoin, then deposit the Bitcoin at Galaxy. The Cashier will automatically convert the Bitcoin to fiat currency (i.e., US Dollars) to be used in your account.
If you have any other questions, feel free to contact our dedicated Bitcoin team anytime on Live Chat or by calling 1-855-535-4947.