Hi Donna,

The catalog they show you at the Family History Centres is the same as the one online through FamilySearch:
familysearch.org/catalog-search

The problem with using this for the first few times is identifying which of the different films of the same parish register would be the best one to order. That's why it is a useful shortcut to use the same film as the one used for another family member's baptism, as given on the IGI.
Or, if the person him/herself appears in the IGI, to use the same film as given there under the batch number.

Sue