It all depends on your setup. For tax purposes though

1. When you receive BTC, the value at the time of reception is treated as normal income in USD

2. When you sell/dispose of/spend BTC, you pay capital gains on that

3. When you spend BTC (for example, on a business purchase), the equivalent USD value is the amount you would deduct as an expense.

The capital gains accounting is the only real difference vs USD. You can use tools like koinly, cryptotaxcalculator, etc for that.