What do you mean by an 'Emulate I/O Module' ?
The 'Generic' module profile is for, well, devices, generally third-party, that don't have a Rockwell defined connection manager that Logix understands.
The 'instance' numbers are how the Logix CPU can communicate via CIP messaging to the 'unknown' target device, and the 'size' parameters specify how many things (bytes, ints, dints) are to be read/written for each instance.
For example, an SSD Drive can be connected via ControlNet, but Logix knows nothing about SSD Drives, so you setup the drive as a 1756-Generic module, and specify the connection parameters like this:
Input: Instance-2, Size-9 (32 bit words).
Output: Instance-1, Size 8 (32 bit words).
Configuration: Instance-4, Size 4 (8 bit bytes).
Do NOT use generic modules to configure test I/O points... that will only cause grief later when you install real modules.