Giving notice
The legal step before a civil or most non-Anglican weddings in England and Wales: you each tell your local register office you plan to marry.
You both attend an appointment in person and bring documents such as passports and proof of address. Notice has to be given at least 29 days before the wedding, and appointments can book up, so it's worth arranging early.
The rules are different in Scotland and Northern Ireland, and for Church of England and Church in Wales weddings, where banns are usually read instead. Check GOV.UK or your local council for your situation.