You probably won’t find any reference to those “Prefix” or “Start/End” in the manual for your device because that’s terminology we use to describe the address mapping.
What you’re likely to find is something describing what Holding Registers or Input Registers are used and what they represent. For example, if the manual said that HR0001 - HR0004 were used to represent some given values, then you might set up a mapping that looked like the following:
Prefix is an arbitrary name of your choosing, one that will show up when you browse the device later to pull in tags.
Start and End are where you define the range you want, and implicitly, how many tags there are for that line in the mapping. A Start of 1 and End of 4 means that you’ll have tags for V1, V2, V3, V4 when you browse.
Modbus Type is where you define how to interpret the values. If your device manual said these are regular Holding Registers then you would just pick Holder Register (Int16). The reason there are so many more types than defined in the Modbus spec is because there are a wide variety of devices out there that have their own way of interpreting the data at a given address.
Modbus Address is the starting address on the device. There Modbus spec defines 2000 Holding Registers, numbered 1 to 2000. An entry of 1 means start 1 at the first Holding Register. Since we have 4 entries (defined by start and end), this line in the mapping means we V1 - V4 are mapped to HR1 - HR4.