If you have filemaker 12, then take a look at the asset starter solution. The "Asset" starter solution will sort by category.
Subsummary (leading or trailing): When you place a summary field in this part, the summary field displays “subsummary” information for each subset of records sorted by the specified break field. The subsummary part can be before or after the body part, depending on the placement on the layout. You can have multiple subsummary parts in a layout.
Sort by Category - color the Leading Subsummary - put the Category Name in Subsummary
Records belonging to the Category will be listed under the SubSummary.
Thank you! I've got it in a nice order and everything is split up in different genres.
One thing thou. The Genre title is also repeated like this
How do i manage to just show once for every genre?
As DavidAnders has already recommended, but the Genre field in a leading sub summary part "when sorted by" Genre. As long as you keep your records sorted by this field, you'll see a category sub heading for each Genre.