There are two main versions of UNIX in use today: System V and BSD. System V is the more popular of the two.
From a user's perspective they are very similar and you are unlikely to have difficulty unless you use more than one type of system. In this case you might notice differences in the structure of the file system or in how certain commands behave. The on-line manual should be helpful if you have problems.
Although UNIXhelp is now based on a System V variant of UNIX, you should see only minor differences in the example input and output if your system is a BSD one.