If you plan to get married or register your civil partnership in the United Kingdom and you are subject to immigration control while in the United Kingdom, you may need to apply for a certificate of approval. In simple words it is the permission to get married in the U.K. you don’t need this certificate if you are settled in the U.K or you are British citizen or EEA national

If you are coming to the United Kingdom from overseas to get married or register your civil partnership, before you can give a registrar notice to marry or register your civil partnership you must have in your passport:

• fiancé(e) entry clearance or
• proposed civil partner entry clearance or
• marriage visitor entry clearance or
• civil partnership visitor entry clearance.

Once you get the certificate to approval, you will need to give a registrar at a designated register office notice to marry or register your civil partnership. Once you are married, you may apply to live in the U.K as a spouse/civil partner of someone present and settled in the U.K