That’s exactly what this forum and community is for. To ask and learn.
If you are using the older 1.x binding I can’t help you much. Havn’t used it at all. I went straight to 2.x binding whitch is still under some final developement. You can find discussion about it in here: Modbus openHAB2 binding available for alpha testing. I know it’s a long thread but if you go with 2.x binding it’s worth reading. For example there you can find hints how to read single bits from holding registers.