iPads can be either Class 1 or Class 2 (depending if they are mounted or not).
To be Class 1 or Class 2, they have to meet those AC120-76 requirements. This is done by subjecting sample iPads (of the same generation/model) for testing, e.g., non-interference tests, rapid decompression tests, etc. Typically, EFB vendors like Jeppesen have already performed AC120-76 tests on a range of sample devices (various iPad models, Microsoft Surface tablets, etc).
The classes refer to hardware. The software are rated according to types (Type A, B, C).
E.g. if you intend to use Jeppesen Type B EFB on iPad Air as a Class 1 device, Jeppesen will give you the required AC120-76 iPad Air test data to submit to the FAA along with paperwork from Apple indicating that the iPad batteries also meet 120-76 requirements, etc.