Cryptocurrencies aren’t legal tender or fiat currency. A share of a cryptocurrency is a capital asset, with no legislated or intrinsic value; it’s worth what people are willing to pay in a market.
If you want cash for your cryptocurrency holdings, you’ll need to sell them. You might realize considerably more than your cost basis, or you may have a loss. For income tax purposes, you recognize a capital gain(loss) and report on Form 1040, Schedule D. Guessing from the tone of your question, you’ll likely need some competent, professional tax guidance to help you.