Census returns from every household in the UK were transcribed into Census Enumerators’ Books (CEBs) by government officials. It is these CEBs that are available to search online or in county record offices. You can search the years 1801 to 1911, with the records from 1851 onwards being the most useful for tracing a marriage. Prior to this date there was no mention of who was married to who, and you will have to take an educated guess that a couple are married where they are shown as living together.
Much of the population was illiterate until the early 20th century, which means poor handwriting and spelling errors were very common. Combine that with transcription errors and it means censuses can be very inaccurate. Don’t be put off if a record doesn’t quite fit; it might be what you are looking for. Try and find the record somewhere else to see if that resolves the inaccuracy.