The `BigInt()` function in JavaScript is used to create a numeric value that can represent integers larger than the maximum safe integer limit, which is 2^53 - 1. This is particularly useful for applications that require precise calculations with very large numbers, such as cryptography or scientific computations. You can create a `BigInt` by passing a number or a string to the `BigInt()` function. To use `BigInt`, simply call it with a number or a string representation of an integer. For example, `BigInt(123456789012345678901234567890)` creates a `BigInt` representing that large number. You can also use the `n` suffix, like `123456789012345678901234567890n`, to define a `BigInt` directly. Keep in mind that `BigInt` values cannot be mixed with regular numbers in operations without explicit conversion.