The IRS classifies cryptocurrencies as a type of property, rather than a currency. If you receive Bitcoin as payment, you must pay income taxes on its current value. If you sell a cryptocurrency for profit, you pay taxes on the difference between the purchase price and the product of the sale. Cryptocurrency tax rates depend on your income, tax filing status, and how long you've owned your cryptocurrencies before selling them.
If you had it for 365 days or less, then you pay taxes on short-term profits, which are equal to income taxes. If you owned it for a longer time, then you pay taxes on long-term profits. If you earn cryptocurrencies through mining, you receive them as a promotion or as payment for goods or services, they are counted as regular taxable income. You must pay taxes on the full value of the cryptocurrency the day you receive it, based on your marginal income tax rate.
Simply buying cryptocurrency with USD or another government-issued currency is not subject to taxation. Nor does it require you to mark “yes” to the cryptocurrency question on your tax return (assuming you haven't done any other reportable activity).