Hi Isabel,
When you get the film number you contact your local LDS family history centre, ask them to get the film in, quoting the number (and pay them, its not a large amount) they will ring your when its in and your go to the centre and view it there on their equipment. They will keep it a few weeks so your can organise a convenient date with them. Thats why I said its a bit of a pain but worth it if you know your are going to look at your ancestors original records.
Finding your local LDS centre will probably depend where in the world you live and I'm not sure how to do it apart from your local county records office - thats how I found out where mine is, they had lots of literature. Perhaps some of the more experienced and knowledgeable people reading this will be able to advise!!
Regards,
Carol