Am new to BLE, now using SDK 110 but could not find any user guide for it?
Depends if you mean SD 110 or perhaps SDK V11.0
I presume you mean Softdevice 110
In which case, you'll need to use SDK 10 and the API reference is here
infocenter.nordicsemi.com/index.jsp
If you want to use the most recent SDK (12.2) you would need to use the S130 Softdevice, as S110 support stopped after SDK 10.
