A hex editor is used to edit binary files in a similar way that text editors are used to edit ASCII files. If you want to use the same program as I used for the screenshots, there is a link to version 7 of Hackman further down in the
Hex editing - gold, experience, stat/skill points topic.
The term 'hex' comes from the use of the hexadecimal system, which uses the numbers 0 to 9 and letters A to F (so 9 + 1 = A). The Window's calculator program can convert between decimal and hexadecimal values.
If you were not already into act 2, and easier way to cheat might be;
Actiontrip.com's Beyond Divinity Cheats - starting a new game with stronger characters
What are you trying to do? Something specific, or did you just want to play around?