You can view marriage certificates in the church register - if the couple got marriaed in a church.
You will have to know which church they got married in.
Then find out where that church register is held (could be still at the church, though unlikely, or at the county archive)
Then visit the place where it is held and view the certificate.
That takes considerable time, petrol money and also at times a lot of effort.
it is easier to search the General register office index of birth, marriages and deaths for the marriage and then order from the GRO.
Free bmd - is not a complete gro index, it is a volunteer transcription that is not complete.
The GRO indexes can be found on ancestry, find my past and at larger libraries and archives - usually searchable for a small fee.
Marriages I would always from the gro, births and deaths can be ordered from the local register office where the event tookplace - you need the year and the persons name, you do not need the gro volume and page number (as the local ofice send the certificates copies to the gro - thus the local office doesn't have the gro indexing system)