The process is explained here:
https://www.topcashback.co.uk/gettingstarted
The withdrawal process is explained here (from TCB's FAQs section):
"[Q] How do I withdraw my cashback?
[A] When your cashback cashback shows as 'payable' in your account, you can withdraw and choose from a wide range of payout methods such as bank transfer, PayPal, or any of our 20+ gift cards for extra bonuses. For most withdraws, we usually pay you within a couple of working days.
Tip: Add your payout details earlier, even before you’re ready to withdraw, as we’d automatically disable payments for 72 hours for security reasons."
(So you're invited to submit your preferred method of payout straight away, through your account settings, but you're not obliged to provide it yet if you don't want to).
If you want to shop in-store, rather than online, you can use OnCard Cashback:
https://www.topcashback.co.uk/help/oncard-cashback