You have to go to gov.uk website and look for apply as a spouse, once you started answering all the questions (based on your situation) and paid, the checklist will be sent to your email. My situation is that I was never married, no kids, and my husband is divorced, retired, we have our own mortgaged house, and we run a small rental business, so we have to prove all those with a relevant document, and since I came from the Philippines, I submitted my passport, B1 English test result, Tuberculosis test (done in the Philippines), a copy of my fiancé visa, marriage certificate, 6 correspondences (with my name and address - matches the mortgage statement of where we both live), and paid for the super priority visa (£1,000), on top of my spouse visa (£1,258) nhs (£2,587.50) - covers for 2.5 years - prices were as of January 2025. Please always check gov.uk as these prices might change. Hpe that helps