Paste your wallet address and it won't receive another fragment from any token on Fragments. No sign-in, no signature, nothing to pay.
Why you got one
Your wallet swapped on pump.fun, PumpSwap or Jupiter recently. Each token's own creator fees paid for the fragment, including the small deposit that opened its token account in your wallet.
What you can do with it
Nothing, if you like. You can also send it on, or burn it and close the token account to get the deposit back. See every send to your wallet on the public ledger.